High-Fidelity Computational Multi-Physics Laboratory: Projects

Leveraging experimental data, turbulence models are assessed for their capacity to capture pressure and heat-flux loads in complex transitional and Shock/Boundary Layer Interactions (SBLIs) environments.

Large Eddy Simulation of supersonic jets impinging on a flat surface replicate the propulsion system of VTOL aircraft in hover. Our research focus is on understanding the turbulent fountain-flow generated underneath an aircraft and the intense sound produced from aeroacoustic resonance. Observations of the hydrodynamic and acoustic coupling of the two jets informs new models that provide insight and prediction of sound intensity over a range of impinging heights and propulsion configurations. 

The transition between ramjet and scramjet operation modes in a dual-mode scramjet is not fully understood. The recent flight test of the HIFiRE 2 provided the opportunity to experimentally study this event. In order to supplement this study, computations were performed to understand the influence of inlet distortion, SBLI, and corner separation during the mode-transition event.

A Semi-Empirical Model of a Nanosecond Pulsed Plasma Actuator For Flow Control Simulations with LES

A phenomenological model, suitable for coupling to Large Eddy Simlations (LES) of flow control applications, is developed to simulate the effects of a nanosecond dielectric barrier discharge (NS-DBD) actuator. The model considers various surface and volume heating profiles to reproduce the key qualitative and quantitative features of NS-DBD actuators. The model is tuned to match the unique wave shape observed in Schlieren imagery and quantitative wave speed and displacement data. The induced wave structure, comprised of a cylindrical component with a tail, can be reproduced with a spatially varying heating distribution - a Gaussian variation in the direction of the discharge provides accurate results. The instantaneous location of the wave, which propagates at approximately acoustic speed after an initial transient may be matched by considering a volumetric deposition model. Power input estimates in the current model are consistent with those postulated in experimental investigations.

Control of transitional shock wave boundary layer interaction using surface morphing

The potential of surface morphing techniques, including passive shock control bumps (SCB) and active surface morphing is explored to control transitional shock wave boundary layer interactions (SWBLI). In addition to reduction of the size of the separation bubble, a key objective is to mitigate the low-frequency unsteadiness that can cause detrimental structural response. To this end, three-dimensional flow simulations are performed using direct numerical simulations (DNS) at Mach 2 and Reynolds number based on inflow boundary layer thickness Re_δin = 996. An incident oblique shock at the shock angle of σ = 35 deg and shock strength of p2/p1= 1.4 impinges on a laminar boundary layer that evolves from a Blasius profile. The boundary layer separation due to the shock impingement leads to G ̈ortler-like instability, where the nominally two-dimensional and steady inflow undergoes flow transition, giving rise to a three-dimensional and unsteady interaction. An aero-structural solver framework is developed and employed to examine surface morphing control. To avoid unrealistic structural deformation in the transient or final states, the structural integrity is concurrently monitored so that the intermediate morphing solutions are restricted to achievable elastic deformation. The results indicate that the transitional SWBLI can be controlled in this manner, to essentially eliminate the three-dimensionality and unsteadiness associated with the G ̈ortler-like vortices. Both passive SCB and active surface morphing reduce separation by modulating the sharp increases in surface pressure at separation and shock-impingement points encountered in uncontrolled SWBLI, without incurring additional loss of the stagnation pressure.

The video shows the effect of active surface morphing on the flow transition exhibited in a shock wave boundary layer interaction, in terms of Q criterion isosurface, completely eliminating the flow separation and transition. The vertical axis is scaled for clarity.