A droplet/wall impact model and simulation of a bipropellant rocket engine

Abstract

Droplet impact on a solid wall contributes to droplet vaporization and cooling on the inner wall. A new droplet/wall impact model is developed and fitted from the experimental data, which takes both kinematic parameters of the impinging droplets and thermal parameters of the solid wall into consideration. The model describes the behavior of droplets after impact and identifies five representative regimes, i.e., stick/spread, suspend, rebound, boiling including breakup, and splash, through the critical Weber number of droplets and wall temperature. To assess the new model, numerical simulations were performed of propellant droplets impacting the wall of a bipropellant rocket engine chamber. A comparison with experimental data shows better predictions of the wall temperature of the chamber than obtained from previous models. A larger number of large-sized monomethylhydrazine and nitrogen tetroxide droplets in the boiling induced breakup and splash regimes break into smaller droplets when using the new model. There are also temperature peaks near the impact points and near the throat. Especially in the throat of the combustion chamber, the new model predicts the wall temperature distribution accurately, offering improved prediction of the combustion chamber and assessing thermal protection of the throat.