Energy Characteristics And Electron Density Distribution Calculation Method Of High Enthalpy Plasma Jet

The purpose of the experimental apparatus for plasma-electromagnetic science of near-space hypersonic target is to conduct correlated electromagnetic experiments under the condition of the plasma jet.The electron density distribution of the plasma jet is an important parameter of electromagnetic experiments.The plasma jet generated by the apparatus has the characteristics of high enthalpy and high electron density.Obtaining the energy characteristics and electron density distribution of the plasma jet through calculation and experimental measurement is the focus of this dissertation.There are a large number of chemical reactions in high enthalpy plasma jets.Chemical reactions bring about changes in various species,which affect transport and thermodynamic properties,and transport and thermodynamic properties affect flow and heat transfer characteristics.Flow and heat transfer will affect the chemical reaction,which determines the electron density.The chemical reaction and the flow field are coupled with each other in the whole area.This dissertation first calculates the change of the mole fraction of each species through chemical reaction,and determines the transport and thermodynamic properties according to the change of the mole fraction of each species.In order to divide the coupling of chemical reaction and flow,the source term and diffusion term of the mole fraction of each species and the energy source term brought by the chemical reaction are determined in advance through the chemical reaction.In the flow calculation process,the scalar quantity of the mole fraction of each species is directly introduced,the mole fraction of each group is calculated through the source term and the diffusion term,and the energy source term brought by the chemical reaction is added to the energy term.The result calculated in this way is more accurate.The research in this dissertation provides theoretical calculation support and engineering application guidance for this apparatus.The research content of this dissertation mainly includes the following four aspects:(1)The experimental apparatus has the characteristics of large temperature span,complex chemical reaction and the flow properties are greatly affected by chemical reaction.According to the characteristics of the apparatus,a multi-chemical reaction transient calculation method suitable for the apparatus and a calculation method for transport and thermodynamic properties in equilibrium and non-equilibrium chemical reaction states are proposed.The chemical reaction of the apparatus in the vacuum chamber is a nonequilibrium chemical reaction that is close to an equilibrium state,and there is a certain error in the result calculated by using the equilibrium chemical reaction.The multi-chemical reaction transient calculation method can be used to calculate not only equilibrium chemical reactions but also non-equilibrium chemical reactions.In the calculation process of the transport and thermodynamic properties of multi-species substances,the empirical equation ignores the changes of transport and thermodynamic properties caused by the change of the mole fraction of each species caused by the chemical reaction,so the calculated the result has a large error.In this dissertation,the change of the mole fraction of each species caused by chemical reaction is added to the calculation,which makes the transport and thermodynamic properties more accurate.(2)The experimental apparatus has the characteristics of high power of inductively coupled plasma power supply,concentrated energy injection area,and the effect of chemical reaction on energy.According to these characteristics,a method for calculating the source and diffusion terms of the energy injection and electron species suitable for this apparatus is proposed.This experimental apparatus generates plasma through inductive coupling,the current on the coil generates a magnetic field,and the magnetic field is used to excite and generate plasma.The excitation energy of the plasma is measured by Joule heating.During the process of excitation and flow of plasma,a large number of chemical reactions are accompanied.The chemical reaction will bring about the absorption and release of energy.According to the situation of the chemical reaction,the energy change caused by the chemical reaction is added to the flow calculation to make the calculation of the energy parameters more accurate.There are many chemical reaction equations of air plasma,and the reaction coefficients of each reaction are very different.When the chemical reaction is directly substituted into the flow calculation,some species will always be at the maximum or minimum value.To overcome these shortcomings,each species mole fraction is added to the flow calculation in the form of a scalar,and the source and diffusion terms of each species mole fraction are calculated in advance.By this method,the molar fraction of each species can be kept in a reasonable range,and the calculation amount is also reduced and the calculation speed is improved.(3)Makes the measurement of heat flux values faster and more accurate by introducing heat losses into the temperature equation and retaining the transient term in the temperature equation.The heat flux value can be measured by a contact method using a slug calorimeter.Due to the high temperature of the plasma jet,the slug calorimeter uses water cooling to cool it down and cannot reside in the jet region for a long time.The measurement of heat flux values is made more accurate by introducing heat losses into the temperature equation of the slug.The transient term is retained in the temperature equation to reduce the temperature response time of the slug,thereby reducing the residence time of the slug calorimeter in the plasma jet region,and finally,the heat flux value can be measured faster and more accurately.(4)According to the size and boundary conditions of the experimental platform,the distribution characteristics of the electron density were calculated,and the calculated results were verified by the measurement method.The purpose of this apparatus is to carry out related electromagnetic experiments in the plasma jet environment.The electron density distribution of the plasma is an important parameter for conducting electromagnetic experiments.It is difficult for an electron density measuring device to obtain the distribution of electron density.In this dissertation,according to the size of the experimental apparatus,boundary conditions,as well as the transport properties,thermodynamic properties,chemical reactions and other conditions obtained earlier,the electron density distribution is calculated.The calculated electron density was compared with the measured electron density,and the results were consistent.The calculation method in this dissertation has certain engineering practical value.In summary,this dissertation determines the transport and thermodynamic properties through chemical reactions,and pre-calculates the source terms and diffusion and energy source terms of the mole fraction of each species.Through the numerical simulation of the entire apparatus,the energy characteristics and electron density are obtained.Calculation method.The calculated results of heat flux,enthalpy and electron density in the energy characteristics are consistent with the measured results.The method in this dissertation has guiding significance for engineering applications,and can provide electron density distribution results for subsequent related electromagnetic experiments.