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Vol13 , No 3 (in progress)
Identification of Flow Physics in a Counter Rotating Turbine
Pages : 767-777
Authors : Subbarao Rayapati,  Govardhan M., 
Flow in a Counter Rotating Turbine (CRT) stage is composite and three dimensional due to the blade geometry of nozzle, rotor 1 and rotor 2 that are twisted along the span, spacing between them, tip clearance provided on rotors and also because of oppositely rotating rotors. Present work analyzes the flow field through the nozzle and rotors at planes taken at various axial chord distances. Blade-to-blade contours and the hub-to-tip plots reveal the actual scenario of flow in the turbine stage. Nozzle and the two rotors are modeled in case of the CRT configuration. Boundary conditions are specified as pressure at inlet of the nozzle and flow rate at the outlet of rotor 2. Total pressure, velocity, entropy and TKE distribution through the blades are used to identify the flow over CRT. Flow through the blade rows is distinguished by effects of boundary layer, secondary flows near the hub, pressure gradient effects, presence of vortical flow structures in the passage and near the tip. Total pressure distribution near the midspan in case of nozzle and rotors show the presence of boundary layers and wake regions. Entropy and TKE contours show the loss regions in all the blade rows. Flow losses are more in rotor 2 than rotor 1. Secondary velocity vectors show the presence of vortex regions in the passage and tip clearance. Blade-to-blade contours of CRT reveal the actual flow scenario surrounding the blades. Hub-to-tip plots show the variations of flow parameters while moving from the bottom to top most position of blade. Thus, the present work identifies the exact flow structure in a counter rotating turbine and paves the way for researchers to negotiate flow losses and improve the CRT performance further.
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The Characteristics of Self-Resonating Jet Issuing from the Helmholtz Nozzle Combined with a Venturi Tube Structure
Pages : 779-791
Authors : miao yuan,  deng Li,  Yong Kang,  Hanqing Shi,  yi hu, 
Self-resonating waterjet is a new type of waterjet technology that has been widely used for many practical applications. In order to further improve the performance of self-resonating waterjet, the Helmholtz nozzle was improved by replacing the upper part of a traditional contract structure with a venture tube one. This composite nozzle of a venturi tube structure and a Helmholtz resonator was proposed based on the working mechanism of self-resonating waterjet nozzles and the instability of cavitation flow in venturi tubes. Furthermore, the results were also compared with those generated by a conventional Helmholtz nozzle under the same conditions. The frequency of the pressure pulsation in the oscillating cavity and at the outlet was obtained and analyzed by the classical Fast Fourier transform (FFT) method. The results showed that the main frequency of the pressure oscillation rises to 2362.78Hz, and the peak and average values of the pressure are increased by 45% and 12.5% respectively at the outlet of the composite nozzle. In the oscillating cavity of composite nozzle, the pressure oscillations in the central region have higher frequencies and amplitudes, while near the wall are reversed.
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Aerodynamic Optimization of Unmanned Aerial Vehicle through Propeller Improvements
Pages : 793-803
Authors : Ahmed ElGhazali,  S. S. Dol, 
This paper aimed at presenting a number of suggested improvements that can enhance the performance of a multi-rotor Unmanned Aerial Vehicle. Evaluating each suggestion in terms of the added benefits and feasibility concluded a final choice, which is incorporating a sinusoidal leading-edge profile to the propeller. This choice was numerically investigated with ANSYS Fluent 16.1 through the SST K-Omega turbulence model. The performance of the modified propeller was assessed by comparing the lift and drag results to the same propeller with a straight leading-edge under the same conditions. Both models were studied at pre-stall and post-stall conditions to see the performance effect with respect to the angle of attack. The findings of this research showed 7% increase in the lift force and coefficient that were associated with the addition of the sinusoidal leading-edge including improved recovery from stall spanning from angle of attack that extends between 10° to 25°. This research also provides more insights into how the delayed stall and improved lift help the multirotor to extend flight time and carry heavier payloads. It allows for the exploration of the inner working of the sinusoidal leading-edge and its relationship with the flow field over the propeller.
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Substitute model and CFD Investigations of a Coalescer in a Three-Phase Crude Oil Gravity Separator
Pages : 805-813
Authors : Zbigniew Krzemianowski,  Marcin Lackowski,  Tomasz Ochrymiuk,  Paweł Flaszyński, 
The flow structure in a three-phase gas-oil-water separator and its performance was the main objective of the presented investigations, for which the Euler-Euler multiphase model to simulate the flow was used. The main assumption of the model is that secondary phases, consisting of oil and water droplets, are mono-dispersed with no coalescence and breakup. The considered separator is a part of the installation operated by a drilling company. In general, the investigation of separation process is very computationally expensive and time-consuming, therefore it is desirable to search for some simplifications in order to be able to carry out engineering analysis of the processes taking place in a separator. Hence, the three-dimensional coalescer was investigated as a porous element in order to find pressure losses dependence on flow velocity, which was required to simulate the existence of coalescers and baffles. As the next step, a transient Eulerian multiphase simulations were carried out for gas-oil-water mixture in a real horizontal gravity separator for two- and three-dimensional case. Required data for calculations was derived from real exploration well. In the two-dimensional case, the worked out dependence of the pressure drop with respect to velocity was used to model the flow through the porous coalescers. In three-dimensional case, the coalescers and baffles were modelled without any simplifications. It was found that general trends can be predicted despite the simplification of the geometrical model in which coalescer and baffle geometries have been replaced by a porous medium. The calculations confirmed that the complexity of geometry requiring time-consuming calculations can be usually replaced by introducing simplifications allowing for engineering analysis of separator operation that is acceptable by the industry, because the basic parameters regarding the separation process can be determined.
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Mitigation of Flow Maldistribution in Minichannel and Minigap Heat Exchangers by Introducing Threshold in Manifolds
Pages : 815-826
Authors : P. Dąbrowski, 
In the present paper, a detailed numerical investigation has been carried out to analyze the flow maldistribution in 50 parallel rectangular cross-section (1 mm depth and 1 mm width) minichannels and minigap section (1 mm depth and 99 mm width) with rectangular/trapezoidal manifolds in Z-type flow configuration. The author carried out numerical investigation with various mass flow rates, namely 0.05 kg/s, 0.1 kg/s and 0.2 kg/s which results in Reynolds number of 1532, 3064, 6128 respectively. A novel approach for the mitigation of non-uniform flow has been proposed introducing threshold at the entrance of the minigeometry section. The conventional case without threshold (as reference) and 1 mm, 3 mm and 7 mm threshold were introduced. The threshold has been employed by making a manifolds’ depth bigger than section’s depth. The maldistribution coefficient can be reduced twice in minigap section or three times in the minichannel section already with the 1 mm threshold as compared to the arrangement without threshold. It is found that rectangular manifold gives lower maldistribution coefficient than trapezoidal manifold which corresponds with actual state of the art. The distribution is more uniform in minichannel section than in minigap section for the same inlet parameters. To obtain uniform distribution of fluid flow should be stabilized already at the inlet manifold, at the entrance to the minichannel or minigap section. That was done by introducing the threshold in the manifolds, which is novelty of this study.
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The Effect of Swirling Air-to-Liquid Momentum Ratio on the Spray and Droplet Characteristics
Pages : 827-837
Authors : Mahenderan Chinnaraj,  Rajesh Sadanandan, 
The effect of swirl flow on the spray characteristics (structure, droplet diameter and droplet velocity) is experimentally investigated for varying air-to-liquid momentum ratios in this work. The diagnostic techniques employed include high-speed shadowgraphy and 1D-PDPA. A commercial pressure swirl injector is mounted in a swirl stabilized model gas turbine burner to investigate the spray characteristics with and without the presence of swirling flowfield under isothermal conditions. In the absence of the injector flow the burner produced a converging-diverging flowfield at the burner exit, influenced by the bluffbody effect near to the exit and the swirling intensity farther downstream. The investigations reveal an unmistakable influence of the swirling flow on the droplet size, velocity and spatial distribution. Under the investigated momentum flux ratios the conical spray structure is altered and the droplets size and velocity at each location changed with the spatial variation in the magnitude and nature of the swirling flowfield. In general fine droplets are produced near to the high velocity air inflow, and coarser droplets in the recirculation zone owing to the longer residence time. The mean axial velocity of the droplet reduced in presence of swirling flow, with the droplets showing negative velocities at downstream locations.
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Experimental Investigation on the Effects of Swirl on the Exit Turbulent Flow Field of an Unconfined Annular Burner at Isothermal and Reacting Conditions
Pages : 839-847
Authors : R Manikandan,  Rajesh S,  Prathap Chockalingam, 
The objective was to study the effect of change in swirl intensities, S=0.4, 0.7 & 1 of the annular swirling flow on the exit flow field of an unconfined annular swirl burner operated at isothermal (only dry air) and reacting flow (premixed methane air mixture) conditions. Reynolds number at the burner’s annular exit based on its hydraulic diameter (D) was kept constant at 4000. Exit flow field at isothermal conditions was measured using planar particle image Velocimetry rig and processed using commercial software. The percentage decay in the magnitude of peak value of axial velocity obtained from its radial profile at a height of 4D from the burner exit with the change in swirl intensity of 1, 0.7, 0.4 and 0 was 65%, 55%, 47.2% and 13.5%. The jet spreading angle was 6.5o for S=0, 8.4o for S=0.4, 9.8 for S= 0.7 and 14.2o for S=1. Recirculation zone was observed only for S=0.7 and 1.0. The width of the recirculation zone was 3D (S=0.7) and 3.4D (S=1) respectively. The normalized reverse mass flow rates estimated were 0.027 for S = 0.7 and 0.058 for S = 1.0. The magnitude of turbulence intensities at wake shear layer was much higher than the jet shear layer due to the presence of recirculation zones for S= 0.7 and 1.0. The integral length scales calculated were varied in the range of 0.06D0.18D for all swirl intensities. Reaction front was identified by deconvoluting the time mean OH* chemiluminescence using Abel inversion method. The flame became shorter and wider with increase in swirl number which was in consonance with the observation of increase in size of recirculation flow in the isothermal flow. The equivalence ratios at which the lean blow out observed were 0.58, 0.6 and 0.62 for S=0.4, 0.7 and 1.
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Transient Numerical Analysis of Natural Convection in Partially Open Cavities Filled with Water near the Density Inversion Point
Pages : 849-860
Authors : Eliton Fontana,  Claudia Capeletto,  Adriano Silva,  Viviana Mariani, 
A transient numerical analysis of natural convection of near-freezing water in a cavity with lateral openings and internal heat sources is carried out to investigate the influence of the heat dissipation rate in the flow configuration. The heat sources were positioned to create buoyancy-opposing and buoyancy-assisted conditions simultaneously and the top and bottom walls are kept at 0◦C. The non-linear dependence of the physical properties with temperature is considered in the governing equations. Based on the heat dissipation rate, six different regimes were observed and classified through a qualitative analysis of the temporal evolution of the velocity and temperature fields. The characteristics of heat transfer for each regime are analyzed to define the most important mechanisms of heat removal. In the upper layer (heated from below), the buoyancy forces eventually overcome the viscous forces and unsteady thermal plumes are formed, in-creasing the heat removal through the openings, while the heat transfer with the top wall is not significant. In the lower layer, the development of wave-like instabilities leads to oscillatory regimes for intermediate heat dissipation rates, while for high dissipation rates a steady convective regime is observed. This behavior increases the heat transfer with the bottom wall, making it much more significant when compared with the upper layer.
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Effect of Viscosities on the Spray Characteristics of Pressure Swirl Nozzle
Pages : 861-870
Authors : Zhaomiao Liu,  Jiayuan Lin,  Huilong Zheng,  Yan Pang, 
The effects of medium viscosity on the spray flow rate, spray Sauter Mean Diameter, droplet velocity and spray cone angle of pressure swirl nozzles are investigated by making use of the particle dynamics analysis system and high-speed photographic system. Based on the axial and radial distribution characteristics of Sauter Mean Diameter and droplet velocity, the water-glycerol mixture is used to simulate medium with a wide range of viscosities. It is found that with the increase of viscosity, the turbulence of the medium flow and the swirling effect is weakened, and the rated pressure becomes larger and the spray flow rate increases. Spray Sauter Mean Diameter and droplet axial velocity becomes larger, while the spray cone angle decreases. The development of the axial velocity distribution of spray cone is characterized by the radial and axial position parameters. The area of the large-droplet region on both sides of spray cone becomes larger, and the area of small-droplet region near the axis becomes smaller.
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Investigation of Air Flow Characteristics in Air Intake Hoses using CFD and Experimental Analysis based on Deformation of Rubber Hose Geometry
Pages : 871-880
Authors : Kemal Furkan Sökmen,  Osman Bedrettin Karataş, 
In this study, the pressure loss value of air intake hose of FIAT 1.3 E6D type engine, located between intercooler and inlet manifold of the engine, was examined using computational fluid dynamics, considering geometrical deformation in a rubber material. The rubber material modelling was performed by the verification of the data - obtained through the experimental method- with ANSYS software using Mooney-Rivlin method. The rubber material modelling was performed with the aim of correctly determination of the increase in the hose diameter when subjected to pressure, since the material has the feature of elasticity. In this study, ANSYS Fluent v.18.0 software and a static pressure machine were used. The air intake into the hose took place at the pressure of 123,5 kPa and flow rate of 0,087 kg/s. A solution, independent of the number of element, was obtained in the analysis. The turbulence model used in the study is standard k-ε type. As a result, the deformation-oriented pressure loss in the last geometry was found 1,85 kPa. The analyses were repeated for non-deformed geometry, and a pressure loss of 2,04 kPa was determined. At the result of the test, the geometry was seen to become actually deformed, and the pressure loss was found 1,9 kPa. The lowness of pressure loss in the deformed geometry was seen as the removal of the sharp bends that would cause local losses with the effect of pressure forces. In this study, it was determined that geometrical deformation changes the geometrical features that causes pressure loss, and leads to less pressure loss.
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Design for a Squirrel Cage Fan with Double Arc Blade
Pages : 881-891
Authors : Zhehong Li,  H. S. Dou,  Peifeng Lin,  Wei kun,  Yongning Chen,  Limin Lin,  Xinxue Ye, 
Squirrel cage fans are commonly used in HVAC (heating, ventilation, and air conditioning) systems. The single arc blade model is commonly used in this type of fans since it can be shaped simply only by two parameters of inlet and outlet angle of blade. However, the efficiency of the fans is much lower than that we expected. In this paper, the single arc blade is replaced by double-arc blade in order to optimize the blade model and to improve the static pressure efficiency and total pressure efficiency of the fan. Numerical results show that the design with double arc blade is able to improve the internal flow, and to enhance the aerodynamic performance of squirrel cage fans.
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Stent Porosity Efficiency in Treating Wide-Neck Saccular Renal Artery Aneurysm
Pages : 893-908
Authors : H. Abu Bakar,  A. Abas,  N. Razak, 
Renal arteries are the arteries that supply blood to the kidneys. Renal arteries are the arteries that supply blood to the kidneys. Renal artery aneurysm (RAA) is the second most common visceral aneurysm to occur, which accounts for 22% of the visceral aneurysm. In general population, RAA rate of occurrence was only 0.1%. However, due to the extensive used of angiography technique, RAA has been discovered more frequently. Some claimed that the previous rate of incidence should be higher now because of the capability of angiography. The rupture of this aneurysm could result in haemorrhage, kidney lost and mortality. The size of the renal artery which is different compared to other types of arteries such as the abdominal aorta could produce different flow condition when the artery is inflicted with RAA condition. Thus, a thorough analysis is desired as RAA studies are very limited compared to other aneurysm conditions. In this study, the efficiency of the stent porosity was investigated in treating the RAA. Fluid-structure interaction (FSI) simulations and particle image velocimetry (PIV) experiments were the approaches taken to investigate the flow patterns of the blood when the stent of different porosities was placed in the aneurysm entrance. The effect of wall shear stress (WSS), the deformation of the artery and von Mises stress were also observed in determining the possibility of aneurysm rupture. The study found that the placement of stent of different porosities succeeds in providing an obstruction to the blood from circulating inside the aneurysm sac. This in turns reduced the WSS experienced by the aneurysm sac up a significant value of 96%. This reduction is crucial in order to prevent the aneurysm from rupture. Moreover, the placement of the stent provided support to the renal artery and preventing it from experiencing buckling failure. The maximum deformation of the artery reduced by 42% with stent was placed in the renal artery. In fact, the von Mises stress decreased below the threshold limit of 0.5 MPa with the presence of the stent. In addition, the study found that the stent of porosity 80% has a similar impact to the stent of lower porosity in the case of RAA at main renal artery.
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Michell’s Thin Ship Theory in Optimisation of Warp-Chine on Pentamaran Configuration
Pages : 909-921
Authors : Wiwin Sulistyawati,  . Yanuar,  Agus Sunjarianto Pamitran, 
This study was conducted to optimise warp–chine pentamaran configurations in wave cancellations to a significant total resistance reduction for a wide range of speed. The optimisation of a pentamaran with a warp–chine hull form was performed by a computer program Godzilla based on Michell's theory and validated by the towing test. The distance parameters of the outrigger were evaluated to select the lowest resistance generated. Computational analysis depended on the Michell–based tool compared to a commercial Computational Fluid Dynamics (CFD). The comparison of the measurement test of the total resistance and Michell's calculation results of all configurations showed a suitable trend, especially at Fn ≥ 0.4. However, it was not satisfactory for CFD trend. The illustrated of far-field wave pattern by the Michell-based instrument also consistent with the wave spectrum that captured in the test. The results of the analysis and observations revealed that the test measurement for all configuration models in the same estimated error (uncertainty) range of the total resistance. This optimisation has confirmed the stagger at the range of 0.36L–0.42L where the front outriggers and the after outriggers not in line of clearance as in arrow formation significant in wave cancellation and resistance reduction.
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Numerical Characterization of Natural Swirling Flame Evolving in Free Environment via FDS: a Comprehensive Investigation of Fires Problems
Pages : 923-934
Authors : mohamed ali thamri,  T. Naffouti,  S. Gannouni,  jamil zinoubi, 
In this paper, a numerical study of a swirling flame generated through the interaction between a central fire and its surrounding fires is performed. A swirling flame can be configured by installing a secondary’s sources surrounding the central source, organized in an asymmetrical manner in order to ensure circumferential entrainment of the central flame by the supply puffs air. An analysis is performed to study this kind of flow. This analysis highlights the different zones that characterize the vertical propagation of a swirling flame; a first zone, close to the fire source, characterized by an acceleration of the flow and an increase of the temperature. A second zone marked by the passage of the temperature by a maximum while changing variation with a net decrease of the flow acceleration and a third zone where the thermal and dynamic fields change and gradually decrease. Moreover, this study shows an axisymmetric flow behavior with two different aspects of its global structure. A central region characterized by a block motion (solid core) where the flow is rotational, characterized by a concentration of vorticity, and surrounded by the rest of the space where the flow is irrotational. Moving vertically away from the active source, results show an attenuation of the axial vortex intensity which is accompanied by a disappearance of movement by block. The centerline evolution of the axial and azimuthal momentum flux enables also to highlight these different aspects of the global flow structure.
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Universal Method for Determination of Leakage in Labyrinth Seal
Pages : 935-943
Authors : D. Joachimmiak, 
This paper presents calculation model enabling determination of the leakage rate in labyrinth seals. Described model is based on the Saint-Venant equation. It includes a new type of flow coefficient, which was determined based on experimental tests and described depending on the Reynolds number and the radial clearance. The structure of this calculation model can be applied to determine the leakage rate in straight through, staggered labyrinth seals as well as with various number of clearances. This model enables determining distribution of thermodynamic and flow parameters of the gas along the seal length. Results obtained from this model were next compared with experimental data for various types of seals. It enabled determination of kinetic energy carry-over coefficient in geometries under investigation. The value of this coefficient was then compared with the value of the coefficient from the Scharrer’s, Neumann’s and Hodkinson’s models. Obtained results indicate that the value of the kinetic energy carry-over coefficient depends not only on the seal geometry, but also on the pressure decrease.
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Effect of Hydraulic Resistivity on a Weakly Nonlinear Thermal Flow in a Porous Layer
Pages : 945-955
Authors : Dambaru Bhatta,  Daniel Riahi, 
Heat and mass transfer through porous media has been a topic of research interest because of its importance in various applications. The flow system in porous media is modelled by a set of partial differential equations. The momentum equation which is derived from Darcy’s law contains a resistivity parameter. We investigate the effect of hydraulic resistivity on a weakly nonlinear thermal flow in a horizontal porous layer. The present study is a realistic study of nonlinear convection flow with variable resistivity whose rate of variation is arbitrary in general. This is a first step for considering more general problems in applications that involve variable resistivity that may include both variations in permeability and viscosity of the porous layer. Such problems are important for understanding properties of underground flow, migration of moisture in fibrous insulations, underground disposal of nuclear waste, welding process, petrochemical generation, drug delivery in vascular tumor, etc. Using weakly non-linear procedure, the linear and first-order systems are derived. The critical Rayleigh number and the critical wave number are obtained from the linear system using the normal mode approach for the two-dimensional case. The linear and first-order systems are solved numerically using the fourth-order Runge-Kutta and shooting methods. Numerical results for the temperature are presented in tabular and graphical forms for different resistivities. Through this study, it is observed that a stabilizing effect on the dependent variables occurs in the case of a positive vertical rate of change in resistivity, whereas a destabilizing effect is noticed in the case of a negative vertical rate of change in resistivity. The results obtained indicate that the convective flow due to the buoyancy force is more effective for weaker resistivity.
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Effect of Different Flow Directions on Drag over Riblet
Pages : 957-967
Authors : Jing Wang,  X. Ren,  X. Li,  C. Gu,  Zhang Mingming, 
Variation in flow direction requires extensive consideration in the practical application of riblet surfaces. However, studies scarcely examine the impact of flow angle α for riblet, which is usually adopted to reduce flow drag. Accordingly, this research conducted large eddy simulation for a wide range of flow angles. We explored the effect of 0° to 90° flow angle on the surface drag change of triangular riblet. The time-averaged statistical data and instantaneous flow details indicated that skin friction is decreased with the increase in α. However, pressure drag increased much faster than the friction decrease. Result revealed that skin friction reduction by 4.537% is obtained when α=0°, and it inhibits turbulence in the spanwise direction. When α≈20°, the total drag reduction disappeared. Within this range, the deviation angle showed little influence on the total drag reduction. When α=90°, skin friction is reduced by 73.3%; however the pressure drag and total drag increased, accompanied by an increased turbulence. The flow must be nearly parallel to the riblet to achieve drag reduction. Otherwise, the transverse riblet is an effective method to increase the drag.
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Numerical Study on a Novel Type of High Gravity Rotary Gas-Liquid Separator
Pages : 969-979
Authors : Zhen Zhang,  Hang Wang,  Jie Ma,  Xiang Ling, 
In textile printing and dyeing industry, a novel type of separator called high gravity rotary gas-liquid separator (HGRGS) is designed, which includes a rotary drum with multi-layer fins and an impeller. First, the structure and separation principle of HGRGS are introduced in this paper. Then, the flow field and separation efficiency are studied by CFD techniques. To ensure the accuracy of the numerical simulation, the results are verified by the available experimental data. Compared with the typical cyclone, the maximum pressure drop reduction rate in HGRGS is 64.7% when the gas enters at 10 m/s. Besides, for droplets less than 5 μm, the separation performance in HGRGS is more efficient and it will be greatly improved by 30% for 1 μm droplets. The numerical results also show that the tangential velocity inside the rotary drum is linear with the radius and the higher the rotating speed, the greater the tangential velocity. Moreover, the maximum tangential velocity between the forced and quasi-free vortex has moved to the vicinity of the outer wall, which is beneficial for droplets to move outward. Additionally, the droplets in HGRGS can be captured with enough residence time owing to the lower axial velocity than that in a typical cyclone.
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A Study on the Effects of EGR and VNT on the Intake and Exhaust Pressure Waves in a High-Pressure Common-Rail Diesel Engine
Pages : 981-991
Authors : Shaohua Liu,  Yongfan Hou,  Bi Yuhua,  Sheng Yin, 
The transient pressure waves in the intake and exhaust systems directly affect the intake and exhaust processes of diesel engines, thus further affecting the combustion process and the performance of diesel engines. The variation rules of the intake and exhaust pressure waves at different engine speeds and loads in a high-pressure common-rail diesel engine were studied. Then, the effects of EGR rate and VNT nozzle opening on the intake and exhaust pressure waves were systematically studied by bench test and one-dimensional simulation analysis. The results show that at 2000 r·min-1 full-load, when the EGR rate increases from 0 to 10%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms of the intake pressure and the exhaust pressure change significantly. The fluctuation intensity of the intake pressure decreases by 58.6%, and the fluctuation intensity of the exhaust pressure increases by 77.2%. As the EGR rate increases from 10% to 30%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms are basically unchanged. The increasing magnitudes of the intake and exhaust pressure fluctuation intensities are 16.6% and 20.5%, respectively. As the VNT nozzle opening increases, the average intake pressure and the average exhaust pressure both decrease. The corresponding phases of the intake pressure wave crest and trough are delayed. The fluctuation waveforms of the intake and exhaust pressure are basically unchanged, and the fluctuation intensities do not change significantly.
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Experimental and Numerical Investigation of Friction Coefficient and Wear Volume in the Mixed-Film Lubrication Regime with ZnO Nano-Particle
Pages : 993-1001
Authors : Reyhane Gholami,  Hossein Ghaemi Kashani,  Mohammad Silani,  Saleh Akbarzadeh, 
One of the most important challenges industry has always been facing is the wear phenomenon. Wear is the cause of huge deteriorations in parts and results in a drop in performance and lifetime of different machines. Therefore, finding solutions to reduce friction coefficient and wear is of special importance. The present research aims at numerical and experimental investigation of friction coefficient and wear in the presence of nano-lubricants. In the numerical section, to tackle different scales of contact components, two sub-models are developed. In the first one, contact of asperities is modeled and the properties of contact surfaces are taken into account. Second sub-model simulates nano-particles in the contact region. Furthermore, a series of experiments are conducted under different loads, speeds, and different values for Zinc Oxide nano-particle weight percent using a pin-on-disk test rig. Results show that predicted friction coefficient and wear volume in theory are reasonably in agreement with experimental results. It was found that adding nanoparticle to the lubricant can be beneficial in terms of friction reduction.
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Implications of Velocity Ratio on the Characteristics of a Circular Synthetic Jet Flush Mounted on a Torpedo Model in Quiescent and Cross-Flow Conditions
Pages : 1003-1013
Authors : A. Kumar,  Arun K Saha,  Pradipta K Panigrahi,  A. Karn, 
A high velocity ratio synthetic jet on an arched surface is of great interest for its potential applications in navy, including torpedo. However, in spite of detailed research on synthetic jets over a flat surface in cross-flow, very few observations have been made on synthetic jets over a surface which is shaped like a torpedo. This study experimentally explores a synthetic jet mounted on a torpedo shaped model in quiescent and cross-flow conditions. Initially, the synthetic jet is characterized for two different diaphragm displacements and at four distinct actuation frequencies in the range of 1 Hz – 6 Hz in a quiescent flow environment. Subsequently, in cross flow, similar study is conducted for three cross-flow velocities ranging from 7.2 – 32 cm/s, at a fixed amplitude of diaphragm oscillations. The measurements are carried out using Laser Induced Fluorescence (LIF) and Laser Doppler Velocimetry (LDV) and the qualitative LIF visualizations are corroborated by the quantitative LDV data. These results indicate that the synthetic jet vortex rings can be grouped as stretched vortex rings and distorted tilted vortex rings. The flow structures primarily depend on the velocity ratio, which is function of cross-flow velocity and frequency of actuation. The flow physics in case of a curved torpedo surface is slightly different as compared to the synthetic jet on a flat surface.
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Analytical Solutions for Unsteady Pipe Flows with Slip Boundary Condition
Pages : 1015-1026
Authors : Anek Pillai,  Manu V, 
In this paper analytical expressions for time-dependent velocity profiles and pressure gradient are obtained for fully-developed laminar flows with given volume flow-rate conditions in circular pipe flows with slip boundary conditions. The governing equations are solved analytically using the traditional Laplace transform method together with Mellin’s inversion formula. The evolution of velocity profiles and pressure gradient for starting and pulsatile flow with slip boundary conditions are analyzed. New simplified expressions and perspectives on velocity and pressure gradient for no-slip and slip flows are obtained from the analytical results. New scalings in starting and pulsatile flows are proposed for pipe flows with no-slip and slip boundary conditions using non-dimensional numbers. Special attention is paid to the effect of slip factor and pulsatile flow frequency on the time-dependent skin-friction factor. Finally, by using the starting and pulsating flow results, analytical expressions of velocity and pressure for arbitrary inflow are obtained by approximating the arbitrary volume flow-rate by a Fourier series
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Resistance Force on a Spherical Intruder in Fluidized Bed
Pages : 1027-1035
Authors : Ali Zaidi, 
Insertion of large objects or intruders into granular material is common both in nature and industrial applications. During penetration due to collision between intruder and granular particles, intruder experiences resistance or drag force (analogy from fluid). In literature, it is extensively studied that in dry packed beds granular drag force increases with the intrusion depth. However, nearly no information is available about the effect of fluidization on the granular drag force and is the main theme of this paper. In this paper, discrete element method (DEM) and computational fluid dynamics (CFD) is used for performing numerical simulations. Simulations showed that granular drag force becomes independent of intrusion depth at incipient fluidization and is a function of Reynolds number. Using the mathematical relation of fluid drag force, granular viscosity of the fluidized bed is calculated. The physics for the fluid like state of granular material and the independence of granular drag force with intrusion depth is explained at the end of paper.
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Effect of Interface Momentum Distribution on the Stability in a Porous-Fluid System
Pages : 1037-1046
Authors : Pengfei Hu,  Qi Li, 
We numerically investigate the linear instability problem of Poiseuille flow in a channel partially filled with a porous medium on the bottom side. We are primarily interested in the influence of the interface momentum distribution including stress continuity and jump interface conditions. A spectral collocation method is applied in solving the fully coupled instability problem arising from the adjacent porous and free channel flows. The results show that the “interface stress coefficient” in a negative range has a larger effect on the trajectory of the eigenvalues than that in the positive range, especially the most unstable mode. Moreover, with a low permeability in the porous region, the interface momentum distribution has less effect on the stability of core flow. And when the “interface stress coefficient” is equal to its minimum negative value, the flow passing through the channel is at its most stable state. If the “interface stress coefficient” varies in a positive range, the degree of fluid stability is predicted to slightly diminish due to stress continuity condition at the interface.
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Numerical Study of Water Vapor Injection in the Combustion Chamber to Reduce Gas Turbine Fuel Consumption
Pages : 1047-1054
Authors : Reyhane Sharafodini,  Mohammad Reza Habibi,  Mohsen Pirmohammadi, 
In this study, the effect of water vapor injection on the flow pattern, temperature contamination and emission of pollutants has been studied. Also, the impact of the spray angle on the axis has been investigated and finally, the effect of fuel type and geometry on the flow variables has been investigated. The results were compared with numerical simulations performed by other researchers and the results showed that they are qualitatively acceptable. The purpose of this work is to investigate the effect of the amount of water vapor on flame and NOx released from combustion. The results showed that with the percentage of water injected, there were significant changes in the temperature and pressure contour patterns of the combustion chamber. The results showed that with the percentage of water injected, there were significant changes in the temperature and pressure contour patterns of the combustion chamber. The results showed that the overall efficiency of the Brighton cycle can be increased in the non-injecting mode from 91% to 95% for the combustion chamber mode by injecting 8% water vapor. Also, an increase of more than 8% of water vapor will not have much effect on efficiency of gas turbine and reduce fuel consumption.
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