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火箭发动机热力计算,一般都假设喷管内的膨胀过程是平衡流动、或假设为凝结流动。在这两种假设条件下可以分别计算出发动机的比冲量。在什么条件下才能采用平衡流假设?在什么条件下又应该采用凝结流假设呢?通常都不作必要的论证。本文应用气体动力学基本方程和化学动力学基本概念,导出了判别平衡流动的准则方程,它可以作为采用平衡流动假设的理论依据。通过对实际导弹发动机的计算证明:现代火箭喷管,一般在收敛段是近平衡流,在扩张段则偏离平衡状态较远。本文提出喷管膨胀过程计算新的概念,即在收敛段按平衡流计算,而在扩张段应按凝结流计算。
Rocket engine thermal calculations generally assume that the expansion process inside the nozzle is a balanced flow, or assumed to be a coagulation flow. Under these two assumptions, the specific impulse of the engine can be calculated separately. Under what conditions can the equilibrium flow hypothesis be adopted and under what conditions should the condensate flow hypothesis be used? The necessary justification is usually not given. In this paper, the basic equations of gas dynamics and the basic concepts of chemical kinetics are used to derive the criterion equation for determining the equilibrium flow, which can be used as the theoretical basis for the assumption of balanced flow. The calculation of the actual missile engine proves that modern rocket lances are generally near-balanced flow in the convergent section and far away from equilibrium in the expanded section. In this paper, a new concept of nozzle expansion calculation is proposed, that is, the calculation is based on the equilibrium flow in the convergent section and the condensate flow in the expansion section.