Experimental Study On The Influence Of Steps On The Hypersonic Boundary Layer Transition On A Cone

Hypersonic boundary layer transition has important effects on the aerodynamic and aerodynamic heats of real aircraft,and has always been a hot topic of related research.Cone is typical experimental models,and thus investigation of its boudary layer trasition is of great significance.And it is also important to study the influence of steps on the hypersonic boundary layer transition on a cone.Therefore,the nano-tracer-based planar laser scattering(NPLS)technology,high frequency fluctuation pressure testing technology and temperature sensitive paints(TSP)technology are used to study the influence of steps on the hypersonic boundary layer transition on cone under different conditions in Ma6 wind tunnel.Firstly,the relevent research on the boundary layer transition on the smooth cone is carried out.In the hypersonic quiet wind tunnel,the streamwise NPLS images reveal the clearest picture of the whole structures in hypersonic boundary layer flow from laminar region,the generation and disappearance of the second mode,to the turbulence.And the flow field fine structure of the sharp and blunt cone under different Reynolds numbers and different angles-of-attack are obtained.The results show that as the unit Reynolds number increases,the transition position is advanced,but the boundary layer transition position of the blunt cone is backwarder than the sharp cone.Under low noise conditions,the cone surface fluctuation pressure under zero angle-of-attack is measured by high frequency fluctuation pressure testing technology.The fluctuation pressure data is analyzed by analysis of power spectrum density(PSD),bandpass filtering and cross-correlation calculation.The development law of the characteristic frequency,amplitude and wavelength of the second mode wave is obtained.The results showed that,the amplitude of the second mode wave increases first and then decays downstream along the flow direction,the characteristic frequency of the second mode waves are gradually reduced,the wavelength gradually increases.The NPLS results are compared with the fluctuation pressure results,which leads to a good agreement.At the same time,it shows that the development law of the second mode wave under low noise condition is consistent with the result obtained in the quiet wind tunnel,but the transition of the boundary layer is obviously advanced.Secondly,the development law of small blunt cone and sharp cone boundary layer with different steps under zero angle-of-attack is studied.The problem of boundary layer transition on a cone with different height forward or backward step are investigated in the hypersonic quite wind tunnel,through NPLS technology and high frequency fluctuation pressure test technology.Under low noise conditions,the fluctuation pressure of small blunt cone boundary layer with 0.5 mm height front and back steps is measured under different Reynolds number conditions.And the NPLS experiment is carried out in the typical state.The fluctuation pressure measurement experiment is carried out on the sharp cones with different height forward or backward steps.The TSP technology is used to study the temperature changes of the 0.6mm height forward or backward steps model and the smooth sharp cone model.The results show that the development of the characteristic frequency and amplitude of the second mode wave along the flow direction is consistent with the conclusion obtained in the smooth cone under each condition.However,in the larger forward step model,the wavelength of the second mode wave does not increase monotonically,but fluctuates.The three methods show that the influence of the backward step on the transition of the boundary layer is significantly greater than that of the forward step.The backward step destabilizes the boundary layer and shifts the transition upstream.The forward step can suppresses the boundary layer and shifts the transition downstream when its height is not large,but as the height increases,the suppresses effect gradually weakens and even destabilizes.Finally,the influence of the steps on the hypersonic boundary layer transition under different angle-of-attack conditions is studied by using the three methods.The results show that The backward step destabilizes the boundary layer and shifts the transition upstream.While the forward step sometimes has a destabilizing effect and sometimes has a suppressing effect.But the influence of the forward step on the development of the boundary layer is much smaller than that of the backward step of the same height.