Simultaneous determination of particle size, velocity, and mass flow in dust‑laden supersonic flows

The particle mass concentration and -mass flow rate are fundamental parameters for describing two-phase flows and are products of particle number, -size, -velocity, and -density. When investigating particle-induced heating augmentation, a detailed knowledge of these parameters is essential. In most of previous experimental studies considering particle-induced heating augmentation, only average particle mass flow rates are given, without any relation to measured particle sizes and -velocities within the flow or any indication of measurement uncertainty. In this work, particle number, individual particle sizes, and velocities were measured in a supersonic flow by means of shadowgraphy and particle tracking velocimetry (PTV). The goals are to determine measurement uncertainties, a particle velocity-size relation, and the spatial distribution of number, size, velocity, and mass flow rate across the nozzle exit. Experiments were conducted in a facility with a nozzle exit diameter of 30 mm, at Ma_inf = 2.1 and Re_inf = 8.2e7 1/m. Particles made of Al2O3 and up to 60 µm in size were used for seeding. Particle mass flow rates up to 50 kg/m2 s were achieved. It is shown that an additional correction procedure reduced common software uncertainties regarding shadowgraphy particle size determination from 14% to less than 6%. Discrepancies between calculated particle velocities and experimental data were found. In terms of spatial distribution, larger particles and a higher mass flow rate concentrate in the flow center. The determined particle mass flow rate uncertainty was up to 50% for PTV; for shadowgraphy, it was less than 17%

Particle mass flow determination in dust laden supersonic flows by means of simultaneous application of optical measurement techniques

Particle mass flow rate and particle mass concentration are key parameters for describing two-phase flows, especially for particle-induced heating augmentation analysis. This work addresses the question of how accurate particle mass flow rate can be determined with three non-intrusive measurement approaches, based on shadowgraphy, particle tracking velocimetry (PTV), and scattered light intensity, in supersonic flows. In terms of shadowgraphy and PTV, the particle mass flow rate was determined by measuring individual particle characteristics, namely particle size, velocity, and density, as well as the measurement volume. The presented shadowgraphy procedure is based on the commercial LaVision DaVis software and additional shadowgraphy corrections. Multiple tests were conducted in the experimental test facility GBK of DLR with varying flow conditions, at a Mach number of 2.1, unit Reynolds number (Re∞) ranging from 5e7 1/m to 1.5e8 1/m, total temperature (T0) ranging from 303 to 544 K, and particle materials, namely Al2O3, MgO, and SiO2, in the size range of 1 to 60 µm. Particle size distributions of Al2O3 and MgO particles could be reproduced with shadowgraphy quite well, while the PTV procedure resulted in non-similar distributions. Pycnometer measurements indicated MgO particle density to be significantly lower than reference values. A DaVis parameter variation analysis resulted in a particle mass flow rate uncertainty of shadowgraphy of up to 30%. The particle mass flow rate uncertainty of PTV is approx. 76%, and the respective uncertainty of scaled PTV and scattered light intensity approach is 28%. The particle mass flow rate, measured with shadowgraphy, is 58% higher than those of the semi-axisymmetric scattered light intensity approach, which can be explained by a higher particle concentration at the injection plane

Experimental investigation of heating augmentation by particle kinetic energy conversion in dust laden supersonic flows

The presence of particles in supersonic flows can cause significant increases in stagnation point heat fluxes (Dunbar et al. in AIAA J 13:908–912, 1975). This effect is commonly named particle-induced heat flux augmentation or just heating augmentation. Heating augmentation can be described as the sum of the conversion of kinetic energy of the particles into thermal energy, characterized by the energy conversion efficiency, also called accommodation coefficient, and the increase of convective heat flux (Polezhaev et al. in High Temp 30:1147–1153, 1992; Vasilevskii and Osiptsov in Experimental and numerical study of heat transfer on a blunt body in dusty hypersonic flow 33rd thermophysics conference, American Institute of Aeronautics and Astronautics, 1999). Although the accommodation coefficient is fundamental for heating augmenta- tion characterization, there is only a small number of experimental datasets for it. This work focusses on the experimental determination of the accommodation coefficient in flow regimes at Mach number 2.1, Reynolds number, based on the probe nose diameter, from approx. 6e5 to 1.8e6, and nominal particle sizes of approx. 20 um. The decrease of particle velocity and kinetic energy flux in the shock layer is measured with highly resolved shadowgraphy for individual particles. The particle kinetic energy flux is decreased by 29% on average by particle deceleration in the shock layer. Negligible kinetic energy fluxes of rebounded particles were measured. The accommodation coefficient is approx. 0.36 for Al 2 O 3 and SiO 2 particles, while it is approx. 0.09 for MgO particles. Hence, it is significantly smaller than the widely used value of 0.7, based on the study of (Fleener and Watson in Convective heating in dust-laden hypersonic flows 8th thermophysics conference, 1973), but in good agreement with values given in (Hove and Shih in Reentry vehicle stagnation region heat transfer in particle environments 15th aerospace sciences meeting, 1977) and (Molleson and Stasenko in High Temp 55:87–94, 2017. https:// doi.org/10.1134/S0018151X1701014X ). No difference between erosive and elastic particle reflection mode was detected on the conversion efficiency. The data from a simplification of the modeling approach of the conversion efficiency for elastic particle reflection by Molleson and Stasenko (2017) are in poor agreement with experimental data

Experimental investigation of high-power laser irradiation of missile materials in subsonic and supersonic flows

The technology of missiles and of their countermeasures is evolving continuously. High-power lasers are an option to encounter these threats. In order to understand their potential in such a scenario, it is vital to investigate the laser effects in the presence of a corresponding aerodynamic environment. Thus, experimental and numerical investigations were conducted cooperatively by Fraunhofer Ernst-Mach-Institut and the supersonic and hypersonic technologies department of DLR. An ytterbium fiber laser system was installed at the supersonic wind tunnel VMK. The laboratory was fit to meet necessary laser safety requirements. Combined subsonic and supersonic flow and high-power laser experiments with flow velocities up to a Mach number of three and a laser power up to 10 kW were realized. Two kind of tests were performed, focusing on laser beam distortion through aero-optical effects and on high-power laser effects, respectively. The interaction effects between aerodynamics, laser radiation and irradiated targets were studied on flat-plates as well as cylindrical and radome targets, simulating generic missile design. Irradiated objects consisted of steel, aluminum, carbon-fiber-reinforced polymer and the ceramic-based composite WHIPOX. While beam distortions were studied with a wavefront sensor, damaging processes were investigated by measuring the perforation time of the targets, as well as via high-speed imaging, thermography as well as Schlieren imaging. Numerical three-dimensional, steady, and uncoupled simulations were performed. The data indicated complex interactions between material, laser beam, and aerodynamics. This investigation can be used as an initial basis for further analysis of laser-material-aerodynamic interactions with respect to missile defense

Modeling Heat-Shield Erosion due to Dust Particle Impacts for Martian Entries

Heat-shield design for spacecraft entering the atmosphere of Mars may be affected by the presence of atmospheric dust. Particle impacts with sufficient kinetic energy can cause spallation damage to the heat shield that must be estimated. The dust environment in terms of particle size distribution and number density can be inferred from ground-based or atmospheric observations at Mars. Using a Lagrangian approach, the particle trajectories through the shock layer can be computed using a set of coupled ordinary differential equations. The dust particles are small enough that noncontinuum effects must be accounted for when computing the drag coefficient and heat transfer to the particle surface. Surface damage correlations for impact crater diameter and penetration depth are presented for fused silica, AVCOAT, shuttle tiles, cork, and Norcoat® Liège. The cork and Norcoat Liège correlations are new and were developed in this study. The modeling equations presented in this paper are applied to compute the heat-shield erosion due to dust particle impacts on the ExoMars Schiaparelli entry capsule during dust storm condition

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

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

Experimental Modeling of Alumina Particulate in Solid Booster: Final Report

The ESA-EMAP project (Saile et al., 2019) is dedicated to the experimental modeling of alumina particulates in solid boosters. The motivation roots in the uncertainty regarding the impact of the alumina particles emitted by the solid rocket motors (SRMs) of European launch systems on the ozone depletion in the stratosphere. This uncertainty needs to be addressed in the face of the expected growth and significantly increased number of rocket launchers as predicted in studies associated with the new space era. For this reason, the ESA-EMAP project focused on the experimental investigation of the particle formation processes and the quantification of the corresponding flow conditions by means of sub-scale tests. The particle formation was assessed from the combustion chamber throughout the nozzle to its final state as it would be expected in the atmosphere. These tests were executed with a solid rocket motor (SRM) mimicking a launch system and operating under flight-realistic conditions with an ambient flow. As it can be seen in fig. 1, this task was accomplished by integrating the rocket motor into a subsonic wind tunnel nozzle of the ’Vertical Test Section Cologne’ (VMK). Numerous measurement techniques were applied to capture the flow conditions and formation of the particles. In detail, the high-speed schlieren measurements were applied to capture the density gradients and the topology of the jet. Spectroscopic measurement methods such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy, alumina emission measurement shed light on the exhaust gas composition and temperature distribution of the jet. The velocity was captured by means of particle image velocimetry, direct image particle size determination, and laser-2-focus (fig. 2). The heat release from the jet was assessed with a Gardon gauge and infrared thermography. Finally, the particle size (fig. 5) was quantified by means of measurements with an aerodynamic particle sizer and rocket plume collector (Maggi et al., 2020). In summary, a vast data base on solid rocket exhaust plume was generated. At three different planes along the path line of the particles, there is now information available on the particle size, the particle velocity, the temperature distribution, the density gradient distribution, and the gas composition of the plume. That data base provides a foundation for further analytical explorations and provides the opportunity to validate models associated with the physics of solid rocket exhaust plumes

Characterization of SRM plumes with alumina particulate in subscale testing

The current paper provides an outline and first results of the ESA-EMAP project. This project pursues activities regarding the experimental modeling of alumina particulates in solid boosters (EMAP). The issue regards the particles residing in the atmosphere after the passage of a launch vehicle with solid rocket propulsion, which might contribute to local and overall ozone depletion. The question is to what extent since the particle size distribution left behind is essentially unclear. For this reason, the ESA-EMAP investigations focus on the characterization of the solid exhaust plume properties for well-defined combustion chamber conditions. Thus, details of the rocket motor assembly, of the developed solid propellant grains, and of first measurement results are provided. The paper presents technical findings concerning the rocket motors and reveals aspects to the feasibility of the applied measurement techniques