The development of disturbances in the boundary-layer transition (BoLT) flight experiment flowfield is investigated using a recently developed “quiet direct numerical simulation (DNS)” approach. By...

Numerical Simulation of Instabilities in the Boundary-Layer Transition Experiment Flowfield

High-speed boundary-layer transition is extremely sensitive to the free-stream disturbances which are often uncertain. This uncertainty compromises predictions of models and simulations. To enhance the fidelity of simulations, we directly infuse them with available observations. Our methodology is general and can be adopted with any simulation tool, and is herein demonstrated using direct numerical simulations. An ensemble variational (EnVar) optimization is performed, whereby we determine the upstream flow that optimally reproduces the observations. The cost functional accounts for our relative confidence in the model and the observations, and judicious choice of the ensemble members improves convergence and reduces the prediction uncertainty. We demonstrate our observation-infused predictions for boundary-layer transition at Mach 4.5. Without prior knowledge of the free-stream condition, and using only observations of wall pressure at isolated locations from an independent computation (true flow), all of the relevant inflow disturbances are identified. We then evaluate the entire flow field, beyond the original limited wall observations, and interpret simulations consistently with data and vice versa. Our predicted flow compares favourably to the true ‘unknown’ state, and discrepancies are analysed in detail. We also examine the impact of weighting of observations. Improved convergence of the inverse problem and accuracy of the inflow amplitudes and phases are demonstrated, and are explained by aid of a simple example from two-dimensional unstable, chaotic convection.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/C518F213AD15D015DCAFEC8233005A8F/S0022112021001725a.pdf/div-class-title-observation-infused-simulations-of-high-speed-boundary-layer-transition-div.pdf

Observation-infused simulations of high-speed boundary-layer transition

Hypersonic Ground Tests With High-Frequency Instrumentation In Support of the Boundary Layer Transition (BOLT) Flight Experiment

Wind-tunnel experiments were performed to quantify boundary-layer instabilities both on and off the surface of a 33% scale model of the U.S. Air Force Research Laboratory/U.S. Air Force Office of S...

https://arc.aiaa.org/doi/pdf/10.2514/1.A34858

Preflight Ground Test Analyses of the Boundary Layer Transition (BOLT) Flight Geometry

Abstract Boundary layer transition over a lifting body of 1.6 m length at $2^\circ$ angle of attack has been simulated at Mach 6 and a unit Reynolds number $1.0 \times 10^7$ m$^{-1}$. The model geometry is the same as the Hypersonic Transition Research Vehicle designed by the China Aerodynamics Research and Development Center. Four distinct transitional regions are identified, i.e. windward vortex region, shoulder vortex region, windward cross-flow region and shoulder cross-flow region. Multi-dimensional linear stability analyses by solving the two-dimensional eigenvalue problem (spatial BiGlobal approach) and the plane-marching parabolized stability equations (PSE3D approach) are further carried out to uncover the dominant instabilities in the last three regions as well as the shoulder attachment-line region. The shoulder vortex is conducive to both inner and outer modes of shear-layer instability, of which the latter most likely trigger the vortex breakdown. A novel method is presented to substantially reduce the computational cost of BiGlobal and PSE3D in resolving the cross-flow instabilities in cross-flow regions. The peak frequencies of cross-flow modes lie between 15 and 45 kHz. Whereas oblique second Mack modes are marginally unstable in the windward cross-flow region, they could be strong enough to compete with the cross-flow modes in the shoulder cross-flow region. In the shoulder attachment-line region, there exists only one unstable mode of Mack instability, differing from previous studies that show a hierarchy of modes in the context of symmetrical attachment-line flows. Results of the numerical simulation and multi-dimensional stability analyses are compared when possible, showing a fair agreement between the two approaches and highlighting the necessity of considering non-parallel effects.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/54A895804688FC34D016E64C75D6EC53/S0022112021011253a.pdf/div-class-title-boundary-layer-transition-and-linear-modal-instabilities-of-hypersonic-flow-over-a-lifting-body-div.pdf

Heather Kostak

Papers

Hypersonic Ground Tests With High-Frequency Instrumentation In Support of the Boundary Layer Transition (BOLT) Flight Experiment

Preflight Ground Test Analyses of the Boundary Layer Transition (BOLT) Flight Geometry

Freestream disturbance effects on boundary layer instability and transition on the afosr bolt geometry

Hypersonic Boundary Layer Off-Body and Surface Measurements on the AFOSR BOLT Geometry

Drag Reduction Initial Conditions on Various Legacy Fleet Aircraft: Surface Roughness Measurements