Measurement and Analysis of Dust-Laden Flow Experiments in the DLR GBK Facility

Abstract

The analysis of dust-laden flows can be an important element of spacecraft design. For example, a spacecraft entering the Martian atmosphere will encounter dust particles suspended in the atmosphere. If the entry occurs during a major regional or global dust storm, dust particle impacts on the heatshield of the spacecraft can cause erosion of the vehicle thermal protection system (TPS) that can be equivalent to that caused by thermochemical ablation [1]. There is also a possibility of particulate matter in the atmosphere of Titan that may impact the Dragonfly project capsule during its atmospheric entry. Vehicles landing on the surface of Mars or on the Earth’s moon may also liberate surface dust or regolith due to plume-surface interaction (PSI) effects [2]. Developing a simulation capability to model dust-laden flows requires the ability to accurately predict the velocity of a particle as it travels through a shock layer, nozzle plume, or the flow of an experimental facility. The primary mechanism that determines the particle velocity is the drag force acting on the particle. The drag force is typically expressed in terms of the frontal area of the particle, its velocity relative to the surrounding fluid, the density of the surrounding fluid, and a non-dimensional drag coefficient. Substantial effort has been devoted over many decades to developing models or correlations to estimate the drag coefficient for spherical bodies over a wide range of flow conditions [3] – [8]. The correlations have historically been based on experimental data, but more recently computational simulations have been used to augment the experimental data [3]. Since 2017 there has been a successful partnership between the NASA Entry Systems Modeling (ESM) project under the NASA Game Changing Development (GCD) program and the German Aerospace Center (DLR). Dusty flow experiments have been performed in the DLR GBK facility [9]. DLR has developed advanced diagnostic techniques in the GBK facility that allow simultaneous measurement of particle size, velocity, and mass flow rate [9]. This new high-precision experimental data is well-suited to drag model validation efforts. An additional element of the ESM project is the development of an integrated CFD-particle trajectory code, named US3D-DUST [10], that uses a Lagrangian-based framework to compute particle trajectories in a dust-laden flow. The GBK experimental data will be used to validate the US3D-DUST code as well as to assess the ability of existing particle drag models to accurately simulate particle trajectories in the GBK experiments