Characteristics Of The Fluctuating Pressure In The Internal/External Integration Flow Of A Hypersonic Vehicle

Shock wave/boundary layer interaction is prominent in the internal and external flow of an air-breathing hypersonic vehicle.Due to the constraint of space and the coupling effect of upstream and downstream boundary conditions,a variety of com-plicated and severe fluctuating pressure environments are formed,which is more chal-lenging than simple external flows.To adapt to the long-time flight during cruise,a reasonable structure design of aircraft requires full understanding of the characteris-tics of fluctuating pressure caused by various shock wave/boundary layer interactions and shock train structures in the internal and external flow,well clarified mechanism of the unsteadiness,and the capability of rapid prediction method of the fluctuating pressure loads.In the present study,the fluctuating pressure sources and fluctuating pressure load characteristics in canonical shock wave/turbulent boundary layer interac-tions were summarized and analyzed,and an fast engineering prediction method was consequently established.The fluctuating pressure characteristics of several complex shock wave/turbulent boundary layer interactions in the inlet/isolation section were in-vestigated in a shock tunnel,and the influence of interaction strength,geometric config-uration and upstream and downstream boundary conditions on the flow characteristics was discussed,and the oscillation mechanism was analyzed.The engineering method is an important method to predict the fluctuating pres-sure loads due to its speediness and high efficiency.For a few typical two-and three-dimensional shock wave/turbulent boundary layer interaction induced separation flow,the fluctuating pressure environments caused by boundary layer turbulence,separation flow and shock wave oscillation are summarized and analyzed.Based on the analysis,with the help of the mean flow parameters,the interaction flow is divided into sev-eral zones.The fluctuating pressure in those zones are predicted separately and then integrated.Thus,an engineering prediction method for the fluctuating pressure distri-bution over the whole interaction is established.The predictions of fluctuating pres-sure loads agrees reasonably with experiments of compression ramps,oblique shock wave/turbulent boundary layer interactions.The present method is effectively applied to the inlet configuration,which provides a reference for the analysis and prediction of the fluctuating pressure characteristics in complex interaction flow.The interaction flow such as the forebody/inlet compression corners and the cowl shock/shoulder interactions are the representative models for the generation of fluctuating pressure environments.Experiments were conducted using the simplified configu-rations.The compression corner experimental results show that the fluctuating pressure loads increase with the interaction strength.The fluctuating pressure predicted by the present engineering method are basically consistent with the experimental results,which further validates the reliability of the engineering method.In the cowl shock/shoulder interactions,the introduction of expansion waves makes the shoulder configuration and impinging point of cowl shock become the important factors.The experimental results of two configurations of the rounded shoulder and the sharp shoulder show that the peak position of the fluctuating pressure loads changes with the impinging point of the cowl shock in the rounded shoulder,and the sharp convex corner restricts the movement of the peak position.The spectral characteristics also indicated that the sharp convex corner has a significant suppressive effect on the low-frequency oscillation of the separation shock.Under the effect of backpressure from the combustor,shock train oscillations in the inlet/isolation section are the important source of severe fluctuating pressure.A engineering method for predicting the fluctuating pressure of forced oscillations of shock train is established,and the prediction of the fluctuating pressure induced by a low-frequency sinusoidal backpressure agrees well with experimental results.Ex-periments were carried out to study characteristics of the shock train oscillations in an inlet/isolation with boundary layer suction.Various throttling ratios were imposed at the cowl-side wall of isolator exit to simulate backpressure.At medium throttling ra-tios of 25.3%?32.3%and high throttling ratios of 35.3%?38.2%,the unsteady shock train presents a large-amplitude low-frequency oscillation mode and a small-amplitude high-frequency oscillation mode,respectively,under the effects of pre-exist background waves and boundary-layer suction in the isolator.In the large-amplitude oscillation mode,a large separation zone foms and vanishes periodically on the cowl-side wall.As a result,on the shoulder-side wall,the leading separation shock of the shock train moves forward and backward repeatedly between the trailing edge of the suction slot and the isolator exit.The dominant frequencies of the large-amplitude oscillation mode are 280?480 Hz,which decrease with the increase of the throttling ratio.In the small-amplitude oscillation mode,a large separation zone on the cowl-side wall persists through-out,whereas the leading separation shock of the shock train oscillates near the suction slots at the shoulder-side wall.The dominant frequencies of the small-amplitude oscil-lation mode are 900?1800 Hz.Both oscillation modes cause severe fluctuating pressure loads in the isolator.