Wall shear rate and its axial and azimuthal components were evaluated in stable Taylor vortices. The measurements were carried out in a broad interval of Taylor numbers (52-725) and several gap width (R1/R2=0.5 - 0.8) by two three-segment electro diffusion probes and three single probes flush mounted in the wall of the outer fixed cylinder.The axial distribution of wall shear rate components was obtained by sweeping the vortices along the probes using a slow axial flow. The experimental results were verified by CFD simulations. The knowledge of local wall shear rates and its fluctuations is of primordial interest for industrial applications like tangential filtration, membrane reactors and bioreactors containing shear sensitive cells.

In this study, flow behind rectangular vane type Vortex generators mounted on a flat plate, is numerically simulated using the immersed boundary (IB) method. In the present work, the direct forcing IB method is employed because of its simplicity and high efficiency. Vortex generators of two different heights are numerically investigated. The height of vanes in the first case is close to the definition of submerged/lowprofile Vortex generators while the other case is closer to the definition of a conventional Vortex generator. The resultant highly three-dimensional flow and its transition to turbulence have been studied. Counterrotating vortices generated by these passive rectangular Vortex generators are characterized. Streamwise evolution of non-dimensionalised maximum values of vorticity, Vortex strength, streamwise velocity and wall-normal velocity are studied. The simulations show that the IB method in conjunction with DNS effectively simulates the time-dependent flow behind an array of passive Vortex generators placed in an initially laminar boundary layer.

To discover the nonlinear characteristics of pipe flow, we simulated the flow as a sum of many Vortex rings. As a first step, we investigated the nonlinear interaction among a maximum of three Vortex rings. The pipe wall was replaced by many bound vortices. A free Vortex ring moves right or left according to the radius, and that of a particular radius keeps the initial position. The energy of a free Vortex ring, except when it is close to a wall, coincides with that without boundaries. Two Vortex rings of equal radii always show a repeated overtaking process. In the case of three Vortex rings, they show a wide variety of behavior. For certain combinations of radii and the axial spaces among them, the motion, which seems to be very complex, is limited on a curved surface in three-dimensional space whose axes correspond to the three radii. It was found that this simplicity comes from the momentum conservation law, and also that its direction depends on the energy contribution calculated from free Vortex rings. Our results elucidate the nonlinear behavior among many vortices.      

To investigate the dynamics of droplet-Vortex interactions in particle-laden Karman Vortex street flows, the simulations were carried out by using Euler-Lagrange approach, which was validated by the available experiments and numerical results. Then, the particle dispersion and the dimensionless frequency (Strouhal number) of the wake flow were analyzed to evaluate the particle-Vortex interactions. The particle dispersion was statistically analyzed from both time and space dimensions and the different instantaneous dispersion patterns were explained by the relative slip velocity. Two independent scaling parameters, Stokes number StL and particle-fluid mass loading ratio Φ were revealed, and the particle mean square displacement and the Strouhal number were modelled by using these two scaling parameters, respectively. Finally, the characteristic lengths of the particle-laden wake flow were researched, and the Strouhal number physical model was developed based on the oscillating fishtail model. The results indicated that, firstly, StL and Φ, which constitute a dominant scaling group, can characterize the dynamics of droplet-Vortex interactions in wake flow. Particles gradually separate from the Vortex with the increase of StL due to the centrifugal effect, and the Vortex intensity and regularity get worse with the increase of Φ, which further disperses the droplets for their momentum exchange with irregular Vortex structures. Secondly, the length of the formation region and the width of the free shear layer diffuse are the two simultaneous characteristic lengths of the Strouhal number in oscillating wake. The proposed Strouhal number model gives a physical basis for the frequency determination, and the predicted errors are within ±1. 5% error bands with mean absolute percentage error of 0. 67%.

Rectangular S-duct diffusers are widely used in air-intake system of several military aircrafts. A well-designed diffusing duct should efficiently decelerate the incoming flow, over a wide range of incoming conditions, without the occurrence of stream wise separation. A short duct is desired because of space constraint and aircraft weight consideration, however this results in the formation of a secondary flow to the fluid within the boundary layer. The axial development of these secondary flows, in the form of counter rotating vortices at the duct exit is responsible for flow non-uniformity and flow separation at the engine face. Investigation on S-shaped diffusers reveals that the flow at the exit plane of diffusers is not uniform and hence offers an uneven impact loading to the downstream components of diffuser. Experiments are conducted with an S-shaped diffuser of rectangular cross-section at Re=1.34´105 to find out the effects of the corners (i.e. sharp 90o, 45o chamfered etc.) on its exit flow pattern. A ‘fishtail’ shaped submerged Vortex generators (VG) are designed and introduced at different locations inside the diffusers in multiple numbers to control the secondary flow, thereby improving the exit flow pattern. It is found that the locations of the VG have a better influence on the flow pattern rather than the number of the VG used. The best combination examined in this study is a 45o chamfered duct with 3´3 VG fixed at the top and bottom of the duct inflexion plane.The results exhibit a marked improvement in the performance of S-duct diffusers. Coefficient of static pressure recovery (CSP) and coefficient of total pressure loss (CTL) for the best configuration are reported as 48.57% and 3.54% respectively. With the best configuration of VG, the distortion coefficient (DC60) is also reduced from 0.168 (in case of bare duct) to 0.141.

It is generally believed that, on slender delta wings, there is a critical state at which strong asymmetric vortices are found along the leading edge on the leeside of the delta wing. These asymmetric vortices can lead to high lateral forces even when slender delta wing is at the zero angle of yaw. Some experimental studies reported recently, cast considerable doubt as to the validity of the above explanations. A wind tunnel investigation was, therefore, performed to study afresh this phenomenon. The flow over four sharp edged delta wings with aspect to a ratio ranging of 0.56 to 1.46 was investigated using flow visualization with laser light sheet and some surface pressure as well as hot wire measurement. The tests were conducted for angles of attack ranging from 0 to 30 deg and at a free-stream velocity of 30m/s corresponding to a Reynolds number of 4.8 × 105 based on the center line chord of the wing. The results obtained suggest the absence of asymmetry in the Vortex core position in the flow.      

A discrete Vortex model coupled with a Vortex dissipation and Vortex core criteria is used to study the unsteady flow past two airfoils in configuration. The unsteady wakes of the airfoils are modeled by discrete vortices and time-stepping is used to predict the individual wake shapes. The coupledflow is solved using a combined zeronormal flow boundary condition and Kelvin condition which result in (2 N+2) X (2 N+2) equations. Results are presented showing the effect of airfoil-airfoil and airfoil-wake interaction on the aerodynamic characteristics of the configuration. The effect of relative velocity, rate of pitching and phase-lag are studied on airfoil performance and wake shape is predicted.

The micro tube bank model is a commonly used structure in microelectro mechanical cooling systems. flow across a micro tube bank is a basic benchmark for analyzing flow resistance and heat transfer capability. In this paper, the flow around a micro tube bank model was studied both experimentally and numerically. Micro-Particle Image Velocimetry technology was used to measure the flow field at different inlet flow rates. The laminar flow model, S-A model and standard k-ε model were used to calculate the flow field inside the micro tube bank model. By comparing the results from the three numerical models with the experimental results, there is a certain gap between them can be noted. However, it was found that the standard k-ε model is better than laminar model and S-A model in the comparison between numerical results and experimental results. In conclusion, the standard k-ε model is more suitable for the numerical calculation of the flow field around a micro scale tube bank model.