Continuing Experimental Studies of High Speed Boundary Layer Transition in LENS Facilities to Further the Development of Predictive Tools for Boundary Layer Transition in Flight

摘要

In working toward a methodology to predict the onset and extent of boundary layer transition in flight from ground test measurements and computational results CUBRC continues to perform experiments and associated computational work to measure boundary layer instabilities in a short duration shock tunnel facility. The experimental studies were performed in the LENS II facility at Mach numbers between 3.5 and 8.0 over a large hollow cylinder flare and large cone flare configurations designed and constructed to study turbulent shock interaction over the flare section. The large scale of these models is intended to produce very large length scale Reynolds numbers and produce a wide spectrum of turbulent scale sizes and eliminate the effects of the boundary layer transition process upstream of the flare interaction region. This large scale is also ideal for boundary layer instability measurements at low Reynolds number due to the production of thick laminar boundary layers upstream of boundary layer transition. The long test times in the LENS II facility (up to 100 ms) also make it a desirable situation for the measurement of boundary layer instabilities. In addition to surface measurements, the CUBRC team has also been actively perusing in stream measurements both inside the boundary layer and in the freestream outside of the shock layer. The boundary layer measurements will be made with high frequency thin-film sensors coupled with newly constructed electronics and optical measurement techniques to obtain similar frequency results that were obtained with the surface pressure sensors. The facility freestream disturbance measurements will then be made with similar techniques. These measurements, along with mean and stability computational results will provide information concerning the boundary layer transition mechanisms and provide one part of the flight prediction methodology. This paper will describe the work at CUBRC performed to date to prepare these techniques for future experimental campaigns. Currently experimental and computational studies mentioned in this paper have been performed on several flight configurations with much success, but as of the writing of this paper the key flight test ground experiments needed for comparison have not taken place. To make this comparison possible CUBRC continues moving forward with experimental and computational studies to compare to flight boundary layer results obtained during the recent HIFiRE-1 and NASA X-43 flight programs. CUBRC currently possesses a full-scale model of HIFiRE-1 flight shape and is planning to retest this shape at actual reported flight conditions and model attitudes with measurements of the location of boundary layer transition on the surface and before mentioned flowfield and freestream measurements of the instabilities. CUBRC also has plans to build a full-scale model of the X-43 flight vehicle and instrument the vehicle leeside with experiments and predictions at key flight boundary layer transition trajectory points as reported recently by Berry. The X-43A flight test program was a remarkably successful program and provides one of the best open literature data sets in recent history containing well defined information on the aerothermal loads present during flight in regions of laminar, transitional, and turbulent flows with both tripped and natural boundary layer transition.