Experimental study of hypersonic boundary layer transition on a flat plate delta wing

•The behavior of boundary layer transition on a delta wing was studied.•Boundary layer transition on side line is earlier than that on center line.•Low frequency large scale structures induce to boundary layer transition.•Nonlinear interaction prior to transition is stronger than turbulent boundary layer.•Unstable region of disturbance waves depends on the Reynolds number. The boundary layer transition on a flat plate delta wing was investigated in the Mach 6 quiet wind tunnel via global temperature and wall pressure measurements as well as flow visualization. The results show that the boundary layer transition on side line is earlier than that on center line, and larger angle of attack promotes the boundary layer transition. As the Reynolds number increases, the transition position of boundary layer moves upstream. The hot streaks on the center line of delta wing at 0° angle of attack which are symmetrically distributed with respect to the center line at 10° angle of attack are suspected to be arised from the vortical flow rather than the boundary layer transition. High frequency disturbances occurring nonlinear phase coupling transfer the energy to low frequency structures, and finally the low frequency large scale structures induce to boundary layer transition. The intensity of nonlinear interaction prior to boundary layer transition is stronger than that in turbulent boundary layer. In addition, the unstable region of disturbance waves depends on the Reynolds number.