Boundary Layer Transition Experiment in a Supersonic Flight

In fluid mechanics, the boundary-layer transition is a very important phenomenon for high-speed flows because it severely affects the skin friction and heating rates on the model surface. The classical correlations for high-speed flows have been developed based on experimental observations in wind tunnels. When the experiments are performed, they are mostly controlled by the flow Reynolds number because the maximum size of the model is fixed based on the size of the test section of a wind tunnel. In most cases, artificial surface roughness is introduced to initiate a transition towards turbulence because of the restricted model size. The flow Reynolds number and Station number on the model surface are crucial non-dimensional indicative parameters that characterize the transition behaviour of the flow. A realistic approach to simulate the effect of model size for studying the boundary layer transition is to conduct a flight test. Against this backdrop, a systematic procedure is adopted to design a generic ogive nose cone-cylinder payload module (0.7 m long) for a boundary-layer transition experiment in a supersonic flight. Nickel thin film gauges are used to infer heat transfer data on the payload module at various locations for 10s flight duration. The heat transfer data from the temperature history are obtained using two different techniques: one-dimensional semi-infinite heat conduction analysis and deconvolution method. The analysis from flight data indicates a peak Mach number of 2.018, which is achieved after 1.157s of flight. The Reynolds number during the flight is of the order of 10 million , which is an indication of completely turbulent flow during flight duration. It is also supported by heat transfer prediction through the Stanton number, which falls in the range of 0.5 to 1.2. It is concluded that the length of the model is not sufficient to initiate a transition towards relaminarization because the Stanton number and Reynolds number variation do not show any drastic change at any of the gauge locations. However, the promising surface temperature histories from nickel thin film gauges during flight are very useful to devise more realistic heat-transfer models for for higher time scales flow duration through inverse heat-conduction analysis and modern machine learning models.

 Speaker: Prof. Niranjan Sahoo

Prof. Sahoo’s research interests lie in high-speed aerodynamics, ground test facilities, measurements for forces and heat transfer, shock waves, and their applications in allied fields, combustion, energy , hydrogen energy and storage. He has been awarded fellowships from DAAD Germany, BOYCAST and Young Scientist Scheme from DSTHe has offered several online courses (Applied Thermodynamics, Power Plant System Engineering, Advanced Thermodynamics and Combustion, Fundamentals of Compressible Flow) on NPTEL platform. He has over 115 Journal Publications, 153 in conference proceedings and 11 Book Chapters.