Abstract:

The problem of boundary layer transition on a cone with forward or backward axisymmetric step is investigated in the hypersonic wind tunnel, through the high frequency fluctuation pressure test technique and the nanoparticle-tracer planar laser scattering (NPLS) technique. The fluctuation pressure data is analyzed by the analysis of power spectrum density and cross-correlation calculation. The development of the disturbance waves in the boundary layer is obtained, and the relevant parameters of the second-mode wave are analyzed quantitatively. The results show that, the amplitude of the second-mode wave increases first and then decays downstream along the flow direction. But the characteristic frequency of the second-mode waves are gradually reduced. The characteristic frequency and propagation velocity of the second-mode wave increase with the increase of the Reynolds number (the characteristic frequency in the backward-step model increases from 100 kHz to 196 kHz, and it increases from 97 kHz to 174 kHz in the forward-step model). However, the wavelength is reversed (the wavelength in the backward-step model reduces from 6.35 mm to 4.54 mm , and it reduces from 7.35 mm to 4.66 mm in the forward-step model). The second-mode wave in the backward-step model appears closer to the upstream than in the forward-step model, and the boundary layer transition position is forwarder than the forward-step model. The NPLS results are compared with the fluctuation pressure results, which leads to a good agreement.

Key words: Cone, Axisymmetric step, Second mode, Hypersonic boundary layer, High frequency fluctuation pressure