numerical simulation

In the present study, using axisymmetric numerical simulation based on the Euler-Euler method, subcooled flow boiling of pure water in a pipe was investigated and the local and average heat transfer coefficient, local and average vapor volume fraction, and local and average wall temperature under different boundary conditions have been investigated. According to the results obtained from the numerical simulations, the wall temperature increases with increasing pressure. Also, the vapor volume fraction has decreased with increasing pressure. The effect of heat flux on wall temperature and vapor volume fraction is greater than all other boundary conditions. Although numerical approaches give a complete insight into the flow pattern and thermal characteristics, the simulation of complex multiphase flows requires high computational resources and is very time-consuming. In conclusion, we present a deep learning approach based on artificial neural networks to predict the mentioned parameters in pure water. The models presented in the present study accurately predict the output parameters using the hyperparameter tuning method. The results of the prediction models show that these models are able to accurately predict the objective functions with an average absolute error of less than 2.5% and a coefficient of determination greater than 0.9.

The purpose of this research is to evaluate a ground test bed of an orbital transmission engine with pre-evacuation of the engine's internal space. In the usual tests on the ground, the initial pressure of the engine is atmospheric pressure. While during the orbital mission, the internal space of the engine may be in the vacuum pressure. Therefore, it is necessary to test the performance by pre-evacuating its internal space. In this research, the suitability of an exhaust diffuser for this type of test is investigated numerically. The unsteady numerical simulations have been done by applying the pressure-time profiles of the engine as the boundary condition of the inlet pressure. Investigations show that the two phenomena of flow being supersonic in the diffuser at very low engine pressures and the discharge of the return flow to the vacuum chamber prevent the significant influence of environmental conditions on the flow inside the nozzle. So, from the initial moment to the stable working of the diffuser, the flow in the first half of the nozzle is in the supersonic state. Therefore, the internal ballistics of the engine is evaluated independently of the conditions of the outside environment.