超临界二氧化碳超声速流动中的激波问题研究

Shock Wave Problems of Supersonic Flow of Supercritical Carbon Dioxide

关键词:  超临界二氧化碳  临界点  超声速流动  激波  激波极曲线

Key words:  Supercritical carbon dioxide  Critical point  Supersonic flow  Shock wave  Shock pole curve

摘要:

对于理想气体而言，激波前后的流动参数变化受马赫数和气体比热比的影响，但对于超临界二氧化碳（S-CO₂），其物性规律在临界点附近变化显著，使得激波后的流动参数难以预估。本文通过推导激波关系式，并结合S-CO₂物性数据库，建立激波计算的数值迭代程序，对S-CO₂超声速流动中的正激波和斜激波进行研究，并将理论分析结果和CFD仿真结果进行对比。结果表明：激波压缩不会造成气态CO₂向液态CO₂转变，但会使得气态或液态CO₂向超临界态转变；CO₂正激波前后压比随马赫数变化主要受来流相态影响，温度比变化则主要受来流初始参数影响；S-CO₂正激波波后参数在不同来流条件下的变化趋势具有相似性，当来流压力在临界压力附近时，波后流动参数变化剧烈；马赫数越高，激波出现最小熵增时对应的来流温度-压力曲线越靠近准临界线；在准临界线两侧，S-CO₂的斜激波脱体角度随来流压力增大分别呈现出“类气体”和“类液体”的变化特性。

Abstract:

For ideal gas， the change of shock wave parameters is affected by the Mach number and specific ratio of freestream， but the physical properties of supercritical carbon dioxide （S-CO₂） change significantly near the critical point， which makes it difficult to predict the flow parameters behind the shock wave. The numerical iteration program for shock wave calculation was established by derivation of the shock wave relation and using the S-CO₂ physical properties data provided by properties database. The normal shock wave and oblique shock wave in S-CO₂ supersonic flow was studied， and the theoretical analysis results were compared with CFD simulation results. Results show that shock compression does not cause gaseous CO₂ to change to liquid CO₂， but causes gaseous or liquid CO₂ to change to supercritical state. The pressure ratio of normal shock changes with Mach number，which is mainly affected by the phase state of inflow， while the change of temperature ratio is mainly affected by the initial parameters of inflow. The variation trends of parameters behind shock wave of S-CO₂ are similar under different inflow conditions. When the pressure of inflow is near the critical pressure， the parameters behind the normal shock wave changes rapidly. When the Mach number increases， the temperature-pressure curve of inflow corresponding to the minimum entropy increase of shock wave is closer to the pseudo-critical line. On both sides of the pesudo-critical line， the oblique shock wave detachment angles of S-CO₂ present the characteristics of “gas-like” and “liquid-like” with the increase of inflow pressure.