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

Abstract

Effects of Rex, Re , Tw=Taw, and Me on the local skin-friction coefficient (Cf ) in a hypersonic airbreathing combustor with various combustion modes were examined. Measurements were performed in the hypersonic airbreathing combustor with airflowMach number and unit Reynolds numbers at the entrance of combustor of 2.5 and 1:6 10 3:5 10 m , 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 Rex, Re , Tw=Taw, and Me. Direct skin-friction measurements were conducted. The state of flow was also surveyed in the streamwise locationwhere skin frictionwasmeasured to attain core-flowparameters, velocity profile, andmomentum thickness. When boundary-layer transition occurred due to combustion, evaluation ofCf by the vanDriestmethod using either by Rex or by Re was not effective. When there was separation with a long oblique shock train and a pseudo shock wave system in the precombustion region due to combustion, evaluation of Cf by the method using Rex was not effective because the origin of the turbulent boundary layer was changed in the downstream combustor.