Boundary Layer Transition on Slender Cones in Conventional and Low Disturbance Mach 6 Wind Tunnels

An experimental investigation was conducted on a 5-degree half-angle cone and a 5-degree half-angle flared cone in a conventional Mach 6 wind tunnel to examine the effects of facility noise on boundary layer transition. The influence of tunnel noise was inferred by comparing transition onset locations determined from the present test to that previously obtained in a Mach 6 low disturbance quiet tunnel. Together, the two sets of experiments are believed to represent the first direct comparison of transition onset between a conventional and a low disturbance wind tunnel using a common test model and transition detection technique. In the present conventional hypersonic tunnel experiment, separate measurements of heat transfer and adiabatic wall temperatures were obtained on the conical models at small angles of attack over a range of Reynolds numbers, which resulted in laminar, transitional, and turbulent flow. Smooth model turbulent heating distributions are compared to that obtained with transition forced via discrete surface roughness. The model nosetip radius was varied to examine the effects of bluntness on transition onset. Despite wall-to-total temperature differences between the transient heating measurements and the adiabatic wall temperature measurements, the two methods for determining sharp cone transition onset generally yielded equivalent locations. In the “noisy” mode of the hypersonic low disturbance tunnel, transition onset occurred earlier than that measured in the conventional hypersonic tunnel, suggesting higher levels of freestream acoustic radiation relative to the conventional tunnel. At comparable freestream conditions, the transition onset Reynolds number under low disturbance conditions was a factor of 1.3 greater than that measured on flared cone in the LaRC conventional hypersonic tunnel and a factor of 1.6 greater than the flared cone run in the low disturbance tunnel run “noisy”. Navier-Stokes mean flow computations and linear stability analysis were conducted to assess the experimental results and have indicated N factors associated with sharp flared cone transition onset to be approximately a factor of 2 lower than that inferred from the corresponding low disturbance tunnel measurements. Nomenclature h heat transfer coeff. (lbm/ft-sec), q/(HawHw) where Haw = Ht,2 H enthalpy (BTU/lbm) k boundary layer trip height (in.) L reference length based on sharp tip model (in) M Mach number N exponential factor in amplification ratio e from linear stability theory P pressure, psia q heat transfer rate (BTU/ft-sec) R or r radius (in.) t time (sec) Re unit Reynolds number (1/ft) T temperature (°F) x axial distance from cone apex (in.) ∗Aerothermodynamics Branch, NASA Langley Research Center, Hampton, VA. ✝ Computational, Modeling & Simulation Branch, NASA Langley Research Center, Hampton, VA. ⊕ Member, AIAA Copyright 2002 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for government purposes. All other rights are reserved by the copyright owner. α angle of attack (degree) φ roll angle (degree) δ boundary layer height (in.) θc cone half angle (degree) Subscripts aw adiabatic wall B blunted nosetip b base e local value at boundary layer edge n model nose ref Fay and Riddell stag. heating (Rn=0.125-in.) S sharp nosetip T transition onset o reservoir conditions 2 stagnation conditions behind normal shock ∞ free-stream conditions w wall Introduction Thermal effects resulting from boundary layer transition during hypersonic ascent, cruise, or entry can represent an important thermal protection system (TPS) design constraint. From a thermal protection perspective, the success of the ceramic-based tiles utilized on the US shuttle orbiter was in some regards the consequence of a conservative (and costly) design philosophy. Strategies for achieving an economically viable next generation space transportation system with