Influence Of Dual-throat Aerodynamic Layout On Hypersonic Ludwieg Tube Wind Tunnel

In order to improve the operation efficiency of conventional hypersonic Ludwieg tube wind tunnel,a fast-acting valve is usually used between the gas storage tube and the Laval nozzle to control the separation of high and low pressure gases.However,the disturbance of fast valve to the incoming flow directly affects the quality of test section flow of the hypersonic Ludwieg tube.To solve the above problems,this work explores the feasibility of a new layout of hypersonic Ludwieg tube.Based on the conventional Ludwieg tube,an additional Laval nozzle and settling chamber can be introduced to improve the quality of the wind tunnel flow field to a certain extent.The main work of this paper includes:(1)By means of theoretical analysis,the basic working principle of dual-throat Ludwieg tube wind tunnel is studied.It is concluded that the start-up and stabilization time of the flow field may be relatively long.(2)Numerical simulation and experiment were used to study the effect of dual-throat configuration on the start-up time of wind tunnel.Firstly,the starting process of double throat Ludwieg tube wind tunnel was studied by numerical simulation.Then,the effects of throat area ratio and settling chamber length on wind tunnel start-up time were studied successively.Finally,the optimal parameters in the numerical simulation were selected for experimental design,and the numerical simulation results were verified by pressure sensor,Pitot rake and schlieren.(3)By means of numerical simulation and experiment,the influence of dual-throat on the quality of wind tunnel flow field was studied without any damping material in the settling chamer.Firstly,the influence of double throat aerodynamic design on the quality of Ludwieg wind tunnel flow field is studied by numerical simulation.Then,the distribution of Mach number in the wind tunnel test section was measured by a Pitot rake,and the pressure fluctuation in the test section was measured by a Pitot probe,so as to study the influence of dual-throat on the quality of static and dynamic flow field in the wind tunnel.In conclusion,the new dual-throat aerodynamic design introduces a settling chamber into the conventional Ludwieg tube without changing the design Mach number.The steady running time and flow field quality can meet the experimental requirements,and the total pressure loss is small.The Laval nozzle can be extended to a larger Mach number by replacing the Laval nozzle.The study confirmed the feasibility of using the double nozzle Ludwieg tube design with the cross-sectional area of the first throat larger than that of the second throat,which could be used to improve the quality of the flow field in the conventional Ludwieg tube wind tunnel.