Vibhav Durgesh

Experimental Investigation of Base-Drag Reduction via Boundary-Layer Modification

This investigation identifies and characterizes the changes in the near wake of a bluff body produced by boundary-layer thickening, which, in turn, result in an overall reduction in the base drag. For this study, wedge and flat-plate models with both smooth and rough forebody surfaces were used. The forebody surface roughness on both models was increased to modify/thicken the forebody boundary layer. Hot-wire surveys were carried out to characterize the boundary-layer state ahead of the separation point, and base-pressure measurements were used to quantify base-drag reduction associated with boundary-layer modification. In addition, particle image velocimetry measurements in the near wake were performed for both models, and proper orthogonal decomposition analysis was used to analyze the velocity data. Low-order near-wake velocity reconstructions obtained from proper orthogonal decomposition analysis accurately represented the near-wake behavior for the studied cases. It was observed from these low-order ...

Multi-Time-Delay LSE-POD Complementary Approach Applied to Wake Flow Behind a Bluff Body

An understanding of the near wake dynamics of a bluff body is desired to better link base drag reduction observed on these bodies with the coherent structures in the wake. This investigation explores different Linear Stochastic Estimation-Proper Orthogonal Decomposition (LSE-POD) methods that can be employed to estimate the dynamics of the energy containing structure. Statistically independent two-dimensional PIV measurements and time-resolved surface pressure measurements are used to determine spatial POD modes and LSE coefficients for estimating the time-varying POD coefficients using measured surface pressures. These results are used with the time-resolved surface pressure measurements to estimate the time-varying POD coefficients that may be used for a low-order, time-resolved reconstruction of the flow field. The multi-time LSE approach formulated in the time domain (multi-time-delay LSE) is found to be successful in capturing the important near wake dynamics.Copyright

Wake Dynamics Resulting from Trailing-Edge Spanwise Sinusoidal Perturbation

The investigation identified and characterized the changes in the near wake of a bluff body produced by trailing-edge spanwise sinusoidal perturbation, which resulted in an overall reduction in the base drag. This study investigated a flat-plate body with an elliptic leading edge and blunt trailing edge, with and without trailing-edge spanwise sinusoidal perturbation. Base-pressure measurements were used to quantify the base-drag reduction associated with spanwise sinusoidal perturbation. In addition, particle-image-velocimetry measurements were performed in the near wake with and without spanwise sinusoidal perturbation, and a proper-orthogonal-decomposition analysis was used to analyze the velocity data. The findings suggest that the spanwise sinusoidal perturbation redistributed the relative kinetic energy, which enhanced the streamwise vortices and suppressed the von Karman–Benard vortices as a result.

Passive Flow Control of a Flat Plate With Trailing Edge Spanwise Sinusoidal Perturbation

The effect of Spanwise Sinusoidal Perturbation (SSP) control method on blunt trailing edge profiled body is studied using simultaneous pressure and Particle Image Velocimetry (PIV) measurements at different vertical and horizontal locations to study the changes in the streamwise and spanwise vortices. Proper Orthogonal Decomposition (POD) is then used to identify changes in the near wake structure associated with coherent energy redistribution due to control. Integral properties such as the base drag and strength of the vortex shedding decrease compared to the base case. The SSP also redistributes the relative energy among different modes, enhancing the streamwise vortices and suppressing the von Karman Benard rolls as a result.Copyright