Abstract
The goal of this study is to present a comparison between different approaches to multiphase injection modeling of self-pressurized rocket engine propellant. Swirled, tangential orifice injector of nitrous oxide, for an “N” class hybrid rocket motor is the object of the study. A brief descriptionof the injector purpose and geometry is provided, followed by a description of different approaches for flow modeling. Examined techniques range from 0D, Homogeneous Equilibrium Model (HEM) to 3D multiphase with mass and heat exchange between phases. Results of analyses are provided and compared with experimental data. The discrepancies between results are of significant magnitude but expected nature. Co clusions about most feasible approaches for engineering calculations are drawn.
Highlights
The object of this study, is an open type swirled injector, being designed for an “N” class hybrid rocket engine (HRE) using nitrous oxide as an oxidizer
Homogeneous Equilibrium Model (HEM) model on the other hand, if discharge coefficient from the incompressible CFD is applied to injector orifice, gives results with significant mass flow rate underestimation (-14.4% on average) even though the orifice flow in the HEM model was assumed isentropic
The orifice of presented injector introduces very high pressure drop on a very short distance what results in huge pressure drop rate above 9 GPa/s for the fluid in that region. This value even left without context, shows why on one side, the HEM assumption of equilibrium between phases is inaccurate, and why for a multiphase calculation impractically high evaporation coefficients are required for which probably the only way to determine them is with experimental results for a physically similar case
Summary
The object of this study, is an open type swirled injector, being designed for an “N” class hybrid rocket engine (HRE) using nitrous oxide as an oxidizer. This kind of injector and it’s more complex versions are commonly used in rocket engines, especially bipropellant engines requiring e↵ective mixing and atomization [1]. Cavitating fluid is injected into the swirl chamber tangentially. Introduced angular momentum causes the fluid to follow cylindrical swirl chamber walls and build up axial velocity. Fluid leaving the swirl chamber has both angular and axial momentum and forms a spray cone
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