Burkard Esser

Transpiration Cooling Using Liquid Water

At the Space Launcher System Analysis (SART) department of DLR-Cologne, a hypersonic spaceplane for passenger transportation is being investigated. A major challenge is the aerodynamic heating of the vehicle. A possible solution for handling the extreme heatloads will be presented. The solution involves an innovative new way of transpiration cooling, using liquid water. The concept has been tested at the arc heated wind tunnel section of DLR-Cologne. The test campaign will be described and the results will be compared with transpiration cooling using a gas as a coolant.

Experimental Verification of Heat-Flux Mitigation by Electromagnetic Fields in Partially-Ionized-Argon Flows

This paper describes an experimental study on heat-flux mitigation within high-enthalpy ionized-argon flows by application of an external magnetic-induction field. Two different axially symmetric test models containing water-cooled magnet coils have been investigated. The models have been made of a material with low thermal conductivity to visualize surface-temperature distribution.The latter has been measured by infrared thermography. Heat-flux rates have been derived from measured front- and rear-surface temperatures, taking into account temperature-dependent material characteristics and considering radiative-cooling exchange to the environment. Flowfield properties have been quantitatively characterized by laser-induced fluorescence, microwave interferometry, emission spectroscopy, electrostatic probes, and pitot probes. In addition, high-quality video recordings and photographs have been taken for shock-layer visualization. Remarkable measured surface-temperature reductions (16 and 44%) and derived heat-flux mitigations (46 and 85%) have been observed in the presence of an externally applied magnetic-induction field.

Comparative Heat Flux Measurements on Standard Models in Plasma Facilities

A comparative experimental study has been performed testing heat flux probes in different European long duration high enthalpy arc heated and inductively heated facilities. Commercial available heat flux sensors, calorimetric probes and SiC probes were used. Tests were carried on three well defined model geometries in stagnation point configuration at two different test conditions defined in terms of specific enthalpy and Pitot pressure. It has been noticed that the reliability of the sensor calibration data is still a major issue. The comparison of measured heat fluxes showed a clear impact of the flow regime (subsonic or supersonic) and enthalpy distribution across the model surface on the results.

Innovative Thermal Management Concepts and Material Solutions for Future Space Vehicles

When entering a planetary atmosphere, space vehicles are exposed to extreme thermal loads. To protect the vehicle’s interior, a thermal protection system is required. Future aerospace transportation demands solutions that exceed the performance of current systems and up-to-date material limits. Therefore, new and disruptive solutions must be envisaged to meet those extreme conditions. In the search of new solutions for sharp leading edges of future hypersonic reentry or transport vehicles, the THOR project, composed of eight European organizations (industries, research centers, and universities) and one Japanese Agency (Japan Aerospace Exploration Agency), is actively working on definition, design, implementation, and simulation of new passive and active thermal management solutions and their verification in relevant environments (high-enthalpy facilities). This paper provides an overview of the recent developments on the four concepts that are targeted in the project, applying different physical methodol...

Fluid Structure Interaction of a Hypersonic Generic Body-Flap Model

The purpose of the present investigation is the validation of a numerical coupling tool for fluid-thermal structure interaction for a generic body flap model by means of experimental data from an arc heated facility. Different geometrical configurations have been simulated and the main coupling phenomena are pointed out. The results show good agreement with the experimental data.

Arc Jet Testing of CMC Samples with Transpiration Cooling

High speed sustained atmospheric flight creates high thermal loads at the tip, leading edges, intake ramps or engine structures of a flight vehicle. However, sharp edges are mandatory for these vehicles in order to obtain the required aerodynamic performance. To provide technical solutions for these problems, the concept of using porous ceramic matrix composite (CMC) materials in combination with active cooling by transpiration was investigated. An arc jet test campaign was carried out to determine basic parameters in terms of minimum required coolant focusing on liquid water as the coolant media. The tests were stagnation tests on flat samples with a diameter of 50 mm. The front wall thickness was 8 mm. The tests were carried out in the L3K and L2K arc jet facilities of DLR Cologne at approximately 1 MW/m² heat load. Good results were achieved in terms of mass flow data for C/C samples. A number of tests could be carried out at low supply pressures and low mass flow. A medium value of the lower limit mass flow is 0.33 g/s at a pressure of 225 hPa which is equal to 0.152 kg/m²s. With aluminum oxide samples, a cold surface could also be maintained, however, it was not possible to establish a steady-state condition in terms of mass flow and supply pressure.

Numerical and Experimental Study of High Enthalpy Flows in a Hypersonic Plasma Wind Tunnel: L3K

In the present study, we describe the end-to-end model of a plasma wind tunnel. A plasma wind tunnel is an useful facility for the ground-based experiment of high enthalpy flows including hypersonic flows, because it can provides a similar flow environment which is experienced by a vehicle during hypersonic flights. For the experimental research of high enthalpy flows, the German Aerospace Center (DLR) Cologne research facility has an arc heated plasma wind tunnel, L3K. The accurate prediction of flow characteristics is very important to calibrate measurement devices and choose measurement methods in a plasma wind tunnel experiment. However, it is difficult to understand the detailed flow conditions of a plasma wind tunnel, because the flow inside a plasma wind tunnel is usually in strong chemical and thermal non-equilibrium state. we numerically simulate a high enthalpy flow inside a plasma wind tunnel using a multi-temperature model and compare with the measured data using CARS method. The numerical model of a plasma wind tunnel will be useful to design a new wind tunnel and determine flow conditions at the test section of a plasma wind tunnel.

Two-Photon Laser-Induced Fluorescence Measurements of Atomic Oxygen Density in Hypersonic Plasma Flow

An experimental investigation of high-enthalpy air flow generated by L2K arc-jet facility of DLR is carried out by means of two-photon absorption laser-induced fluorescence (TALIF) measurements of ...

Plasma flow modeling for Huels-type arc heater with turbulent diffusion

In this study, we developed an analytical model for the flow field in the Huels-type arc-heated wind tunnel (L2K) of the German Aerospace Center. This flow-field model can be used to accurately reproduce the discharge behavior in the heating section and expansion in the nozzle section of L2K. It includes the radiation transport and turbulent flow as well as thermochemical nonequilibrium models, which are tightly coupled with electric field calculations. In addition, we considered the turbulent diffusion model for the mass conservation of the species and performed numerical simulations for several cases with and without the turbulent diffusion model. Computations were conducted to obtain the general characteristics of an arc-heated flow containing an arc discharge and supersonic expansion. We verified that radiation and turbulence play important roles in the transfer of heat from the high-temperature core flow to the outer cold gas in the heating section of L2K. In addition, we performed parametric studies...

Characterization of High-Enthalpy-Flow Environment for Ablation Material Tests Using Advanced Diagnostics

For reliable material qualification in high-enthalpy flows, detailed characterization of material and flow parameters is essential. Therefore, the flowfield of arc-heated facility L3K, which has be...