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The development of microfluidic media supporting blood flow is significant for many applications. Prefractal models have considerable potential for contributing to the study of flow in these media, since information about scale complexity is captured by a small number of parameters. Flows of power law fluids, Bingham fluids and described by the marginal zone theory are considered. In this study, physically based models for estimating the permeability of a microfluidic porous materials are presented. Models are derived assuming that media are represented by a bundle of tortuous capillary tubes with fractal pore-size distributions. They are expressed in terms of porosity, microstructural parameters and fluid characteristics. Expressions for the flow resistance through single tortuous tubes, and the relationship between fluid velocity through tortuous tubes and through straight tubes, in terms of fractal dimensions, are also obtained.

The flow structure transition of a hypersonic inlet from unstart to start during accelerating trajectory is studied by numerical simulation. The results of pressure distribution along the inlet wall, mass flow rate, total pressure recovery coefficient and aerodynamic forces simulated by the quasi-steady and unsteady two dimensional and three-dimensional quasi-steady methods are compared. Analysis indicates that the two-dimensional quasi-steady and unsteady simulations can get the consistent inlet self-starting Mach number, and unsteady simulation can capture the periodical change of aerodynamic forces while this phenomena is not found in quasi-steady simulation. Due to the consistency between the quasi-steady and unsteady in self-starting Mach number in our strategy, for the self-starting process of hypersonic inlet with variable free stream condition, three-dimensional quasi-steady method can be used to approximate the real self-starting process during the acceleration of the aircraft climb, which can greatly save the computational time and improve simulation efficiency.

In this paper, a numerical investigation was conducted on a subsonic compressor rotor with blade angle slot casing treatments. The purpose of the investigation is to reveal the influence of axial overlap of blade angle slot on the compressor stability. Six kinds of blade angle slot casing treatments with different axial overlap rates were investigated in this paper. The results show that with the increasing of axial overlap rates, the stall margin improvement firstly increased and then decreased. And the optimal blade angle slot can obtain 62.51% improvement of stall margin. The flow field analyses show that the bleeding flows formed inside slots can restrain the adverse tip leakage flow, which is the critical factor making the onset of the rotor stall. With the increasing of axial overlap rate of the slots, the relative position between bleeding flows in the slots and tip leakage flow plays an important role in the stall margin improvement.

The electrical characteristics and electrohydrodynamic (EHD) flows in a wire-plate electrostatic precipitator with six shaped discharge electrodes are analyzed by employing the commercial software ANSYS FLUENT with the aid of User Defined Function (UDF). The results show that the corona position of the discharge electrode plays important roles in generating space charge distribution. When the inlet velocity is relatively low, the vortexes induced by the secondary flow exist not only in the downstream of the discharge electrode, but also in the vicinity of the collecting plate. The vortex near the collecting surface in the Knife-shaped system produces the highest recirculation velocity and turbulence intensity, and covers the widest region among the six configurations. For the high inlet velocity, the local recirculation and high turbulence by the secondary flow near the collecting plate in the all six channels disappear but still remain in the downstream of the discharge electrodes, and the airflow in the central region of the six channels would be accelerated. The highest vortex strength and turbulence intensity and the strongest speed-up effect occur in the center of the channel with the Knife-shaped discharge electrode compared with the cases of the other five systems.

The benefits of circumferential groove casing treatment on the performance of a low-speed contra-rotating fan are investigated. Three-dimensional, time-dependent simulations are carried out with the k-ω SST-SAS hybrid turbulence model using the open-source CFD library OpenFOAM. The numerical model is validated with experimental data from the contra-rotating fan with a smooth casing. This comparison showed a very good agreement. Then, two casing treatment variations are analyzed: 1) circumferential grooves on top of the front rotor, and 2) circumferential grooves on top of the rear rotor. Simulating the performance curve at design speed reveals an increase in pressure rise for casing treatment at the front rotor of up to 4 %. This results from significantly reduced blade pressure fluctuations and weakened blade tip vortices at the front rotor. A weaker tip leakage vortex leads to a less disturbed inflow for the rear rotor and thus pressure fluctuations. In contrast, grooves on top of the rear rotor offer no positive effect since there is no rotor downstream to benefit from reduced fluctuations or weakened tip leakage vortex. Pressure probes downstream of the rear rotor were evaluated using FFT. Grooves reduce the magnitude of blade passing frequencies and their harmonics while partly increasing lower frequencies.

Cavitation occurred in hydraulic machines can generate severe pressure fluctuations and induce high-pitched noise. Ventilated cavitation (inject air into the cavitating flow) is one of the most effective ways to control cavitation and then alleviate the noise and fluctuations. Thus, the evolution of ventilation cavitation around a NACA0015 hydrofoil was numerically investigated with a modified model. The results indicated that the ventilated cavitation consists of two parts: the attached cavity which attached to the leading edge of the hydrofoil and the detached cavity which detached from the hydrofoil surface. With the air injection increased, the detached cavity becomes larger. Besides, the ventilated cavity evolves periodically along with two opposite vortexes which fall off in turn near the tailing edge of the hydrofoil. Among three ventilation volumes, an air injection of 250 L/min presents the best alleviation on pressure fluctuation induced by cloud cavitation. The acoustic analysis indicated that air injection is an effective way to alleviate the cavitation induced noise. With air injected into the flow, two new types noises induced by the ventilated cavitation has been detected by monitoring points along the upper side and behind of the hydrofoil: the lower frequency noise induced by the waving of attached cavity and the higher frequency noise induced by the shedding of the detached cavity. While with the air injection increased, both of the two types noises increased. The acoustic and dynamic patterns under different air injection conditions are able to provide guidance in engineering application.

The majority of condition monitoring techniques employed today consider the acquisitioning and analysis of structural responses as a means of profiling machine condition and performing fault detection. Modern research and newer technologies are driving towards non-contact and non-invasive methods for better machine characterisation. Yet current literature lacks investigations into the monitoring and detection of anomalous conditions using fluid dynamic behaviour. If one considers unshrouded rotors which are exposed to a full field of fluid interaction such as helicopter rotors and wind turbines amongst others, such an approach could potentially be beneficial. In this work, time-dependent fluid dynamic data is numerically simulated around a helicopter tail rotor blade using URANS CFD with the Open FOAM software package. Pressures are probed at locations in the field of the rotor and compared to results attained in an experimental investigation where good correlation is seen between the results. A blade is modelled with a seeded fault in the form of a single blade out of plane by 4°. Comparisons are drawn between the blade in its ‘healthy’ and ‘faulty’ configurations. It is observed that the fault can be detected by deviations in the amplitudes of the pressure signals for a single revolution at the probed locations in the field. These deviations manifest as increases in the frequency spectrum at frequencies equivalent to the rotational rate (1 per revolution frequencies). The results described are assessed for their fidelity when the pressure is probed at different locations in the domain of the rotor. Deviations in the pressure profiles over the surface of the blades are also seen for the asymmetric rotor configuration, but may prove too sensitive for practical application.

A mesh-free numerical model based on the Radial Basis Function Differential Quadrature is introduced to simulate the hydrodynamic response of the dam-reservoirs-foundation system affected by earthquake acceleration. The governing equation of the hydrodynamic pressure of reservoir-dam system was discretized using the presented model in an arbitrary shape, semi-infinite domain which truncated by different far-end boundary condition. For this purpose, the effects of fluid compressibility and energy absorption at the reservoir boundaries were considered simultaneously. The presented model was used to calculate the hydrodynamic pressure distribution on dam face caused by earthquake acceleration in several practical examples and the obtained results were compared with available well-known analytical solutions. The comparison demonstrates that the accuracy and efficiency of the presented model are quite satisfactory.

In this paper, a test system based on the Nano-tracer Planar Laser Scattering (NPLS) technique for studying time evolution of unsteady flow structures was finished. Based on this system, the experimental study on the interactions between the incident shock wave and the turbulent boundary layer of the incoming wall was performed. The experiments were performed in a Mach 3.4 supersonic low-noise wind tunnel at the unit Reynolds number of 6.30 × 106/m-1. For the first time, five frames of temporal-correlated fine structure images of transient flow field with shock wave and the turbulent boundary layer interactions (SWTBLI) were obtained under the experimental conditions, and the spatiotemporal evolution characteristics of the flow structure were analyzed. At the same time, the flow field characteristics of temporal-correlated images were studied when the density boundary layer thickness of incoming turbulent layer is δ1 = 0.55δ, δ2 = 0.72δ, δ3 = 0.87δ respectively. During the development of vortex structure in the boundary layer from turbulent boundary layer to separation bubble, the oscillation interval distribution law of induced shock wave was summarized, and the group velocity of vortex structure development in the boundary layer and the relationship between boundary layer thickness and physical space size growth law of separation bubble under different incoming turbulent boundary layer thicknesses were obtained. The results also show that with the increase of the incoming boundary layer thickness, the group velocity in the development process of vortex structure in the turbulent boundary layer does not change significantly. As the thickness of the boundary layer entering the separation bubble increases, the overall growth height of the separation bubble also increases.

A continuous wavelet transform (CWT) is used to detect the most important scales governing the dynamics of a turbulent wall jet flow that evolves through a backward facing step. Our particular interest is the region downstream of the step. The fluctuating velocity signals obtained experimentally by a laser Doppler anemometer at different heights from the wall are first analyzed in Fourier space by performing the density energy spectra (PSD). In the recirculation zone, we noticed that the flow loses its equilibrium when we approach the wall. This is obviously due to the complex nature of flow dynamics which exhibits a complex structure with various scales. Then, we applied the CWT with two wavelet functions: the eighth derivative of a Gaussian which is selected on the basis of the wavelet entropy measures and a Morlet wavelet. The first one is used to locate the more energetic structures and the second to detect the dominant frequencies of the high energy structures. It turns out that, in the external zone characterized by the presence of intermittent eddies; most of the energy is concentrated in the large scale structures. In the shear layer, different scales of structures are observed. We can also observe the physical phenomena such as extension or breakup of structures. In addition, the relative wavelet energy is applied to give the energy distribution at each scale. On the other hand, the Morlet wavelet is used in order to monitor the dragging of large structures characterized by a low frequency (large scale) originating from the wall-jet's external region towards the reattachment region. It is shown that the energy of these eddy structures decreases along their dragging.

The present investigation is focused on the effect of cowl porosity on the performance of supersonic mixed compression air intake. Four different cases (namely 4.4 %, 5 %, 5.5 % and 7.2% of total cowl area) of cowl porosity at three contraction ratios of air intake have been studied. The pattern of the cowl porosity (Square shape) is chosen symmetrically along the span in the longitudinal direction from the cowl tip. Commercially available software Ansys is used in the computational studies to solve the RANS equations with the k-ω STD turbulence model. Various performance parameters of supersonic air intake are obtained and discussed. Excess amount of flow spillage appears near the cowl tip, which is responsible for the standing strong bow shock wave just before the throat for the uncontrolled case (Clean Model). The minimum energy losses and starting behavior of supersonic air intake are captured at 7.2 % cowl porosity for the contraction ratio of 1.25, which reveals the overall improvement in the flow physics and performance parameters. An increase of 32.73 % in the total pressure recovery is observed for 7.2 % cowl porosity at design contraction ratio of 1.25. All the simulations are performed at three contraction ratios of 1.22, 1.25 & 1.31.

Most of the biological ducts which considered to be elastic in nature are layered and possess different fluid properties from that of pumped fluids Best & Taylor (1958). A mathematical model is presented according to the two-layered blood flow in an artery. Such flow demands a two-fluid model with elastic boundary. In addition, biofluids such as blood can be described well using two-fluid models rather than single fluid model. In the present paper, the flow of a Jeffrey fluid in contact with a Newtonian fluid is considered. The expressions for velocity of core and peripheral fluids and the flux flow rate are derived. The effect of the peripheral layer on the fluid motion and pumping characteristics is presented. The core and peripheral fluid velocities along with interface velocity are obtained in terms of inlet, outlet and external pressure; Jeffrey parameter, ratio of viscosity and elastic properties. The results obtained from the present analytical study of flux variation considering elastic properties are in good comparison with the published literature. It is concluded that the elastic parameters significantly affect velocity and flux. Further, it is also found that flux reduces with increase in viscosity ratio. The analysis of the interface velocity on various physical parameters may be useful in understanding the behavior of the blood flow in normal and pathological states.