Abstract
At Université Libre de Bruxelles (ULB), research was performed on a 1 kN lab-scale Hybrid Rocket Motor (the ULB-HRM). It has a single-port solid paraffin fuel grain and uses liquid N2O as an oxidizer. The first Computational Fluid Dynamics (CFD) model of the motor was developed in 2020 and improved in 2021, using ANSYS Fluent software. It is a 2D axisymmetric, two-phase steady-state Reynolds-Averaged Navier–Stokes (RANS) model, which uses the average fuel and oxidizer mass flow rates as inputs. It includes oxidizer spray droplets and entrained fuel droplets, therefore adding many additional parameters compared to a single-phase model. It must be investigated how they affect the predicted operating conditions. In this article, a sensitivity analysis is performed to determine the model’s robustness. It is demonstrated that the CFD model performs well within the boundaries of its purpose, with average deviations between predicted and experimental values of about 1% for the chamber pressure and 5% for the thrust. From the sensitivity analysis, multiple observations and conclusions are made. An important observation is that oxidizer related parameters have the highest potential impact, introducing deviations of the predicted operating chamber pressure of up to 18%, while this is only about 6% for fuel-related parameters. In general, the baseline CFD model of the ULB-HRM seems quite insensitive and it does not suffer from an excessive or abnormal sensitivity to any of the major parameters. Furthermore, the predicted operating conditions seem to respond in a logical and coherent way to changing input parameters. The model therefore seems sufficiently reliable to be used for future qualitative and quantitative predictions of the performance of the ULB-HRM.
Highlights
In order to study the flow in Hybrid Rocket Motor (HRM), the fundamental partial differential equations (PDEs) of fluid dynamics have to be solved, such as the well-known Navier–Stokes equations, which describe the conservation of momentum
Since 2010, the Université Libre de Bruxelles (ULB) and the Royal Military Academy (RMA), both located in Brussels, are working together on a lab-scale HRM
The level of uncertainty introduced in the numerical results; The overall robustness of the numerical model; How the flowfield is affected qualitatively; How the ULB-HRM would react to changing boundary conditions
Summary
A Hybrid Rocket Motor (HRM) is a type of chemical rocket motor. Chemical rocket motors are characterized by the reaction of a fuel with an oxidizer at some point in the motor. Depending on the way in which the fuel and oxidizer are stored, three types of chemical rocket motors exist: liquid, solid, and hybrid rocket motors (HRMs) [1]. HRMs can be throttled, shut down, and restarted [3] Despite these promising properties, HRMs still lack technological maturity compared to solid and liquid systems, which are widely used for space launch, commercial and military applications. An important technological factor contributing to the renewed interest is the research on liquefying fuels such as paraffin wax These fuels form a liquid layer at the fuel surface during operation, which can lead to the formation of roll waves from which fuel droplets can be entrained. Fundamental work on this is done by [4]
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