Research Projects

Boundary layer transition in hypersonic flows remains one of the most critical yet least understood phenomena affecting high-speed vehicle design. Transition from laminar to turbulent flow greatly increases skin friction drag and heat flux, placing severe demands on thermal protection systems and aerodynamic margins. Reliable prediction of transition onset is difficult because it depends on multiple interacting factors, including freestream disturbance intensity, surface roughness, cone geometry, thermodynamic state, and Reynolds number. Existing test facilities often exhibit unavoidable freestream noise, masking the natural development of second-mode instabilities that dominate transition in realistic flight. As a result, empirical correlations derived from noisy tunnels are limited in accuracy and poorly generalizable to actual flight conditions. This project is motivated by the need to generate high-fidelity experimental data under controlled, flight-representative disturbance environments to improve predictive understanding of hypersonic boundary layer transition. The core scientific objective is to quantify the unified, multi-parameter dependence of local transition Reynolds number (Re_(x_T)) on freestream disturbance intensity, surface roughness, cone semi-angle, total pressure, and temperature. The hypothesis is that by systematically varying these parameters in a quiet, well-characterized facility, it will be possible to map transition onset with enough precision to build predictive, data-driven models that outperform traditional empirical correlations and support advanced vehicle design. To test this, the hypersonic Ludwieg tunnel at IIT Hyderabad will be modified to support controlled variation of freestream disturbance intensities ranging from noisy (~2%) to ultra-quiet (~0.02%) regimes, matching high-altitude conditions. The tunnel will include configurable flow straighteners, mesh screens, boundary layer suction systems, and precision-engineered nozzles to minimize wall roughness effects. The design will allow variation of upstream total pressures (1–10 bar) and temperatures (300–500 K) to achieve unit Reynolds numbers typical of hypersonic flight (~10⁶–10⁷). Conical models with semi-angles (2°–7°) and controlled surface roughness (0.02–1.5 μm) will be fabricated to study geometric and receptivity effects. The experimental plan adopts a full-factorial design covering ~3000 test conditions spanning combinations of disturbance intensity, Reynolds number, cone angle, surface roughness, and thermal state. High-fidelity diagnostics, including nano-pulse laser-based Schlieren imaging (~10 ns pulse width), will visualize second-mode instability growth and accurately identify transition locations. Validation will be performed with Particle Image Velocimetry (PIV), while unsteady Kulite® pressure transducers, fast-response wall-mounted thermocouples (CSJT K-type), and a three-axis Kistler force balance will measure surface pressure, heat flux, and drag. The outcome will be a validated experimental database capturing transition behavior under realistic flight conditions, paired with advanced machine learning models for predicting Re_(x_T) as a function of all relevant parameters. These models will provide designers with reliable tools for assessing transition onset, reducing conservatism in thermal protection systems, and improving aerodynamic efficiency. Beyond immediate defense and aerospace applications, the project will deliver a fully modified, quiet-capable Ludwieg tunnel as a national research asset for long-term studies in hypersonic transition physics.