| Drag reduction of hypersonic vehicle has always been a key problem hindering the development of hypersonic aerocraft field.At present,the research in this field is mainly carried out from passive and active drag reduction.Passive drag reduction depend on the properties of materials,by reducing drag and reducing the flow of heat to the aerocraft during the collision.Because of the long period and slow development of research in this aspect,the thermal reduction of materials alone is not enough to guarantee the safety of aircraft under hypersonic speed.Active drag reduction mainly relies on the installation of shock needle,energy deposition and counterflowing on the head of the aircraft.These methods can be manually controlled.Due to their good controllability and easy operation,they have become a research hotspot in the field of drag reduction and heat reduction of hypersonic aircraft.In this paper,the drag reduction and heat reduction of the reverse jet flow and the drag reduction under the combined action of the magnetic fluid and the reverse jet flow are analyzed mainly from the perspective of the reverse jet flow and the addition of magnetic fluid.In this paper,based on Navier-Stokes Reynolds equation,numerical simulation method is used to analyze drag reduction and heat reduction under counterflowing jet.Firstly,a comparative experiment was conducted between the non-jet flow and the jet flow according to the experimental parameters in the literature to verify the reliability of the calculation method in this paper.Then,the influences of the Mach number,jet temperature,nozzle size and jet pressure ratio on drag reduction and heat reduction of the spherical head of hypersonic vehicle were analyzed respectively.In the process of analysis,the modal change of flow field was found.When the spout-pressure ratio gradually increased,the flow field would change from long penetration mode to short penetration mode.After that,the reasons and process of this phenomenon were analyzed,and the specific position of critical spout-pressure ratio was found.All of these studies contribute to a deeper understanding of the use of counterflowing for drag reduction.In order to further study the effect of magnetic field on drag reduction of hypersonic vehicle,a dipole magnetic field was added on the basis of the original reverse jet flow.Firstly,the accuracy of the numerical simulation method after the addition of magnetic field was verified by using experimental data in literature.Then,when the magnetic field was changed and the electrical conductivity was increased,it was found that the backflow area in the flow field increased significantly,which effectively reduced the frontal resistance of the bulb head.In addition,on the basis of adding magnetic field,the influence of jet Mach number and jet pressure ratio on shock wave detachment distance and leading edge resistance of hypersonic vehicle is further studied.It is found that the increase of jet Mach number and jet pressure ratio can effectively reduce the resistance,and the influence of changing jet pressure ratio on magnetic field is greater.The above research shows that the combination of magnetic field and reverse jet can effectively reduce drag.When studying the drag reduction of reverse magnetosurface jet,it is found that the flow field will have different modes when the spout pressure ratio is constant and the magnetic field size is different.In order to further understand the change mechanism of flow field modes,the position change of critical spout-pressure ratio and the change rule of the resistance at the front edge of the ball head during this process,this paper obtained the resistance coefficient under different working conditions by changing the magnetic field and spout-pressure ratio.The results show that the critical spout-pressure ratio shifts back after the addition of magnetic field.When the spout pressure ratio is fixed,the increase of magnetic field is beneficial to the decrease of drag coefficient. |
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