Research On Conversion Mechanism Of Unstart Modes Of Supersonic/Hypersonic Inlets

In this thesis,critical unstart modes were classified based on deep analysis of critical unstart modes during the self-starting process of supersonic/hypersonic inlets.The key influencing factors and conversion mechanism of the critical unstart modes were studied.Moreover,the influence of the relative throat height of internal contraction portion and three-dimensional effect on the self-starting ability of the supersonic/hypersonic inlets were analyzed.Firstly,the self-starting process of seven typical two-dimensional supersonic/hypersonic inlets with different speed ranges was studied using quasi-steady numerical simulation.The conversion process of the critical unstart flow-fields were studied and the influence of unstart modes on self-starting ability were analyzed.Results show that: with the increase of inviscid designed self-starting Mach number,the difference between the viscous critical unstart flow-field and the inviscid unstart flow-field assumed by Kantrowitz theory becomes larger.When the viscous critical unstart flow-field is in the supersonic mode,the viscous self-starting Mach number is higher than the inviscid designed self-starting Mach number slightly.When the viscous critical unstart flow-field is in the middle mode,the viscous self-starting Mach number is smaller than the inviscid designed self-starting Mach number.The viscous self-starting Mach number is significantly higher than the inviscid designed self-starting Mach number when viscous critical unstart flow-field is in the hypersonic mode.In the hypersonic critical unstart mode,the key parameters in the viscous unstart flow-field deviate far from those in the inviscid unstart flow-field,which indicates that Kantrowitz theory and other theories based on Kantrowitz theory are not capable of predicting the self-starating ability of hypersonic inlets.Secondary,two-dimensional simplified inlets were designed and its accelerating self-starting process was simulated to study the influence of internal contraction ratio,cowl compression angle and relative thickness of the boundary layer on the critical unstart modes.Results indicate that: in the range of the research,cowl compression angle has slight influence on the critical unstart modes,whereas internal contraction ratio plays a key role.The conversion of critical unstart modes can be realized if the key influencing factors are altered.The internal contraction ratio,cowl compression angle and relative thickness of the boundary layer all play important roles in the conversion between the supersonic critical unstart mode and the transitional critical unstart mode.The cowl compression angle have no influence on the conversion between the transitional critical unstart mode and the hypersonic critical unstart mode.Lastly,according to different critical unstart modes,three typical inlets were selected to study the influence of relative throat height and three-dimensional effect on the self-starting ability of the supersonic/hypersonic inlets.Results show: relative throat height and three-dimensional effect have some influence on the self-starting ability.For hypersonic inlet,the influence is more remarkable;the self-starting Mach number is more close to that of two-dimensional model if the aspect ratio is greater.