Effect of Local Flow Parameters on Skin-Friction Coefficient in Hypersonic Airbreathing Engines

摘要

Effects of Re_x, Re_θ, T_w/T_aw, and M_e on the local skin-friction coefficient (C_f) in a hypersonic airbreathing combustor with various combustion modes were examined. Measurements were performed in the hypersonic airbreathing combustor with airflow Mach number and unit Reynolds numbers at the entrance of combustor of 2.5 and 1.6 × 10~7 -3.5 × 10~7 m~(-1), respectively. The ranges of total temperature, total pressure of airflow and fuel equivalence ratio were varied, i.e., 1000-2000 K, 1.0-1.8 MPa, and 0-0.4, respectively, to change Re_x, Re_θ, T_w/T_(aw), and M_e. Direct skin-friction measurements were conducted. The state of flow was also surveyed in the streamwise location where skin friction was measured to attain core-flow parameters, velocity profile, and momentum thickness. When boundary-layer transition occurred due to combustion, evaluation of C_f by the van Driest method using either by Re_x or by Re, was not effective. When there was separation with a long oblique shock tram and a pseudo shock wave system in the precombustion region due to combustion, evaluation of C_f by the method using Re_x was not effective because the origin of the turbulent boundary layer was changed in the downstream combustor.