| The nozzle wall of the aerospace engine received the heat flux from the hot gas, is one part of the engine working in high temperature, and its intensity of the infrared radiation of the nozzle is highest at the cruising state. Since the skin friction drag and the convective heat transfer can be reduced when the wall is covered by a layer of plasma controlled by externall magnetic fields, a new method of using the plasma controlled by externall magnetic fields to separate the hot gas from the wall was proposed. The heat flux to the nozzle wall was decreased, then the temperature of the nozzle wall was reduced, so was the infrared radiation using this method. On other hand, the plasma jetting from the nozzle would wrap the hot gas jet, which could absorb and scatter the electromagnetic wave. The characteristics of flow and heat transfer of the gas and magnetic controlled plasma in the nozzle and the jet wrapped by the plasma were studied numerically.The magnetic induction equation was used to solve the induced magnetic field, and the induced current was derived from the Ampere's law. The induced current interacts with the magnetic field to generate the Lorentz force. The additional source terms standing for the electromagnetic effects on the turbulence kinetic energy and turbulent dissipation rate were added in the turbulent model to evaluate the effects of the magnetic field on the turbulence. The mixture model was incorporated into our code to deal with the interface of the gas and plasma. The magnetic induction equation and the modified turbulent equations were solved by the scalar transport solver of FLUENT. The well-known Hartmann flow was simulated successfully by this code to validate the code first. Then, the velocity profiles, volume fraction, temperature profiles, turbulence intensity and the wall temperature varied with the Hartmann numbers were simulated. The results showed that the mixture of the plasma with the gas, the turbulent intensity of the plasma and the heat flux to the wall were attenuated with the increasing of magnetic strength, so that the temperature of the nozzle wall was reduced. With increasing the Hartmann number, the skin friction coefficient was decreased, the velocity profile departured much more from the logarithmic region. The larger the magnetic strength is, the less the wall temperature rise. When the Hartmann number is over 30, the anisotropy of the flow becomes notable. The Nusselt number increased slightly then dropped down quickly with the increase of magnetic strength in the plane of the magnetic field vector; while in the plane perpendicular to the magnetic field vector, the Nusselt number decreased with the increase of the magnetic strength. The volume fraction of the plasma that wrapped the jet was larger and the jet core region was shorter when the plasma jetted out from the nozzle with higher magnetic strength. When the Hartmann number equals to 50, the wall temperature decreased 20.2%, and the length of the jet core region shortened by 21.1% compared with the one without applied magnetic field.The characteristics of flow and heat transfer for the plasma controlled by the applied magnetic field in the convergent nozzle were also simulated. The results showed that the plasma volume fraction decreased as the flow accelerating in the convergent nozzle. Increasing the magnetic strength could improve the plasma volume fraction near the wall, and separate the hot gas from the convergent nozzle wall effectively. The magnetic field reduced the skin friction of nozzle wall, so the thrust coefficient was increased. The thrust coefficient increased 0.74% by the 1.3T magnetic field than that without field. The volume fraction of the plasma that wrapped the jet increased 24% when the inlet plasma mass flux changed from 0.0188kg/s to 0.0265kg/s.
|
PDF Full Text Request