The transition between the Regular Reflection (RR) and Mach Reflection (MR) phenomenon impacts the design of the supersonic and hypersonic air-breathing vehicles. The aim of this paper is to numerically investigate the dynamic transition from RR to MR of unsteady supersonic flow over a two-dimensional wedge, whose trailing edge moves along the x-direction upstream with a velocity, V(t) at a free-stream Mach number of M∞ = 3. The simulation is conducted using the unsteady compressible inviscid flow solver, which is implemented in OpenFOAM®, the open-source CFD tool. Further, the wedge motion is applied by moving the mesh boundary, performing the Arbitrary Lagrangian-Eulerian (ALE) technique. In addition, the sonic and the detachment criteria are used to define the dynamic transition from RR to MR during the increase of the wedge angle. Different reduced frequencies, κ, in the range of [0.1–2] for the moving wedge are applied to study the lag in the dynamic transition from the steady-state condition. The results show that the critical value of κ = 0.4 distinguishes between the rapid and gradual lag in the transition from RR to MR. In addition, the transition from RR to MR occurs above the Dual Solution Domain (DSD), since the shock is curved downstream during the rapid motion of the wedge.

The noise of flow over tandem cylinders at Re D = 22 000 and its reduction using single dielectric barrier discharge (SDBD) plasma actuators are simulated numerically both to confirm and extend experimental results. The numerical approach is based on large-eddy simulation (LES) for the turbulent flow field, a semi-empirical plasma actuation model, and Lighthill's theory for acoustic calculation. Excellent agreement between LES and experimental results is obtained for both the baseline flow and flow with plasma control in terms of wake velocity profiles, turbulence intensity, and frequency spectra of pressure fluctuations on the downstream cylinder. The validated flow-field results allow an accurate acoustic analysis based on Lighthill's equation, which is solved using a boundary-element method. The effectiveness of plasma actuators for reducing noise is clearly demonstrated. In the baseline flow, the acoustic field is dominated by the interaction between the downstream cylinder and the upstream wake. Through suppression of vortex shedding from the upstream cylinder, the interaction noise is reduced drastically by the plasma flow control, and the vortex-shedding noise from the downstream cylinder becomes equally important. At a free-stream Mach number of 0.2, the peak sound pressure level is reduced by approximately 16 dB. This suggests the viability of plasma actuation for active aeroacoustic control of airframe noise.

In the present study, a multi-variable comparative study of the effect of microchannel heat sink configurations on their thermal performance is conducted by numerically simulating three-dimensional fluid flow and heat transfer in multiple microchannel heat sink configurations. Thermal analysis is performed to investigate a novel wavy-tapered channel configuration of microchannel heat sinks with directionally alternating coolant flow for high-end electronics cooling. Simulations were conducted at different tapering and aspect ratios, focusing on how effectively previously proven geometric enhancements combine with one another in novel ways. Results confirmed the superiority of wavy channels over straight channels due to the development of the secondary flow (Dean Vortices), which enhance the advection mixing and consequently the overall heat sink thermal performance. Moreover, width-tapering of the wavy channel showed improved channel performance in terms of thermal resistance compared to untapered wavy channels. Almost 10% improvement in thermal resistance is obtained with width tapering. Also, the thermal performance showed a strong dependency on channel aspect ratio. Overall performance suggests that optimum tapering and aspect ratio conditions exist. The numerical investigations are then extended to novel heat sink design includes wavy tapered microchannels with directionally alternating flow to improve heat sink thermal performance. A 15% reduction in thermal resistance and highly improved substrate surface temperature distribution uniformity are obtained using alternating flow compared to corresponding parallel flow channels.

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