Sebastian Karl

CFD Analysis of the HyShot II Scramjet Experiments in the HEG Shock Tunnel

Testing of the HyShot II scramjet configuration was carried out in the High Enthalpy Shock Tunnel Goettingen, HEG, of the German Aerospace Center, DLR. Computational fluid dynamics (CFD) is applied to support the analysis of experimental results and for the prediction of the free stream conditions in the HEG test section. Numerical simulations of the flow in the complete HyShot configuration for fuel on and off conditions were performed. This paper describes the laminar and turbulent modeling approaches for the CFD analysis and presents numerical results and their comparison to the experiment for both the HEG nozzle flow and the turbulent reacting flow in the HyShot Scramjet. The practicability of pressure-length scaling was tested by using further numerical analysis. Limits of applicability of this scaling approach were identified and are discussed in this paper

An Experimental Investigation of Steady and Unsteady Combustion Phenomena in the HyShot II Combustor

A series of experiments has been carried out in the HEG facility (High Enthalpy Shock Tunnel, Gottingen) to obtain detailed measurements on the HyShotII scramjet configuration under both steady and unsteady combustion conditions. Standard pressure measurements are performed, but a main focus of this campaign is the use of optical and visualization techniques: high-speed visualizations of OH* chemiluminescence together with pulsed-diode laser Schlieren imaging are employed to gain information about the approximate flame location as well as the interaction between the flow features and combustion characteristics. In particular, this allows an unprecedented level of insight into the transient combustioninduced phenomena present in the combustion chamber at high equivalence ratios. Measurements are compared with computational data obtained from the DLR TAU code. I. Introduction

Ground Testing of the HyShot II Scramjet Configuration in HEG

Ground based testing of the HyShot II supersonic combustion ramjet flight configuration was carried out in the High Enthalpy Shock Tunnel Gottingen, HEG, of the German Aerospace Center, DLR. The main focus of these investigations was to obtain surface pressure and surface heat transfer data on the intake and the cowl and body side surfaces of the combustion chamber and the nozzle. Further, high speed flow visualisation of the combustor flow was performed. Two HEG operating conditions which are related to 33km and 27km flight altitude were applied. Computational fluid dynamics (CFD) was applied to support the analysis of the experimental results and for the prediction of the free stream conditions in the HEG test section.

High Enthalpy Cylinder Flow in HEG: A Basis for CFD Validation

Basic aerodynamic configurations are well suited to study fundamental aspects of high enthalpy flows. A test campaign of the flow around a cylinder has been performed in the High Enthalpy Shock Tunnel Gottingen, HEG. Measurements of the density distribution in the shock layer as well as surface pressure and heat flux were taken. The flow in the shock layer is subjected to various relaxation phenomena and therefore the presented measurements provide a useful basis for the validation of physico-chemical models used in CFD codes. This paper presents results of the test campaign and comparisons of measurements to the numerical computations. The sensitivity of the CFD results to different parameters of physico-chemical models is also discussed.

Computation of radiative and convective contributions to Viking afterbody heating

This paper investigates the hypothesis that the observered gap between CFD and thermocouple-derived flight measurements for afterbody heating of the Viking spacecraft can be accounted for by infrared radiation from CO2 molecules in the wake flow. The DLR TAU code is implemented to simulate the Viking I spacecraft at an altitude of 37.4km on a flow-adapted hybrid 3D grid with radiation- flowfield coupling. The radiation spectrum of the CO2 molecule is represented by a statistical narrow band model and radiation transport is calculated via an opacity-binned ray-tracing model. The calculated total heating level on the aluminium base cover is in good agreement with the flight data, while the total heating level for the fiberglass cover is overpredicted. Furthermore, radiation-flowfield coupling is found to reduce the total heat flux on the vehicle surface by up to 10% compared to when radiation is treated in an uncoupled manner.

CFD Analysis of Unstart Characteristics of the HyShot II Scramjet Configuration in the HEG Shock Tunnel

Ground based testing of the generic HyShot II scramjet configuration was carried out in the High Enthalpy Shock Tunnel Gottingen, HEG, of the German Aerospace Center, DLR, and computational fluid dynamics (CFD) was applied to support the analysis of the experimental results. In the present article, the extension of previous numerical analyses which focused on the HyShot II design condition (equivalence ratio of approximately 0.3) to unsteady flow situations in the combustor is discussed. With increasing fuel equivalence ratio, a transition from steady to unsteady flow was observed experimentally. In the framework of scramjet engine design it is of particular interest to identify and to correctly predict the limiting operating conditions, e.g., engine unstart. Therfore, in conjunction with the test campaign performed in HEG, a parametric CFD study was performed utilizing the DLR TAU code to investigate the onset of unsteady combustor flow. Unsteady Reynolds averaged Navier-Stokes (URANS) computations were performed for off-design equivalence ratios above 0.6. I. Introduction ue to the complexity of the flows in air-breathing propulsion systems of future hypersonic flight vehicles and inherent limitations of related ground-based and flight experiments, the application of CFD is mandatory to gain further insight into internal and external flow properties of such vehicles. Detailed flow analyses as well as load and performance predictions obtained by CFD analysis are required to support the design process. However, CFD predictions of compressible turbulent and reacting flows as present in scramjets require the application of complex physical and chemical models, and involve uncertainties which must be quantified.. Therefore, a strong link between CFD, ground based and flight experiments is needed to improve the understanding of the relevant flow physics and to further validate and improve the applied CFD tools. The objective of the work presented in the present article is to apply the DLR TAU code for the numerical analysis of experimental investigations of the HyShot II scramjet configuration which were performed in the free piston driven shock tunnel HEG of the German Aerospace Center, DLR. The experimental data was used as a benchmark to assess the accuracy and reliability of different CFD modeling strategies for internal scramjet flows. In turn, complementary CFD analysis has shown to provide valuable additional information for better interpretation of the experiments. Following previous detailed analysis 3,4 of the engine performance at the design conditions for a flight altitude of 27 km and at an equivalence ratio of approximately 0.3, the results which are presented in the present article focus on the prediction of the unstart characteristics and the operation limits of the HyShot II combustor at large (off-design) equivalence ratios.

Numerical investigation of Dual Bell Nozzle Flow Field

The flow field of a cold flow dual bell has been numerically simulated with the DLR TAU code. The two operation modes and the transition from one mode to the other are investigated by varying the nozzle pressure ratio. A cold flow test campaign on a sub-scale nozzle model yields experimental data for validation of the simulation. Pressure measurements along the nozzle wall and schlieren optics provides information on the flow field in the nozzle. In addition, the models have been successively shortened to allow the observation of the shock system in the vicinity of the contour inflection.

High Speed Flow Visualization at HEG

The High Enthalpy Shock Tunnel Gottingen (HEG) of the German Aerospace Center (DLR) is one of the largest free piston driven shock tunnels capable of simulating high temperature effects in re-entry flows. Full utilization of such a ground based high enthalpy impulse facility, with typical test times in the order of a few milliseconds, requires detailed knowledge of the test section flow, and its starting process. Further, the temporal development of the model flow must be known in order to assure that a steady flow field has developed during the test time window. Therefore, in addition of time resolved model surface property measurements such as pressure and heat transfer, a high speed shadowgraph and schlieren system was implemented at HEG. For the first tests with the new system a cylinder flow was chosen. The large shock stand-off distance of the cylinder flow allows high spatially resolved optical measurements. Due to the sensitivity of the shock stand-off distance to the gas composition, the measurements are also a valuable aid in detecting driver gas contamination in the test section. The results presented in this paper are related to HEG operating condition III (h 0= 13.4 MJ/kg, p 0= 48.3 MPa, Ma=8.7, u ∞=4776 m/s, T ∞=694 K, p ∞=687 Pa, ρ ∞ = 3.255 g/m3).

Numerical Model for Nozzle Flow Application Under Liquid Oxygen/Methane Hot-Flow Conditions

A numerical study is conducted to investigate the impact of different chemical reaction mechanisms on the behavior of reactive nozzle flow. Therefore, a 66-step chemical reaction mechanism for oxyg...

Free Flight Testing of a Scramjet Engine in a Large Scale Shock Tunnel

The free flight force measurement technique is a very attractive tool to determine forces and moments in particular in short duration ground based test facilities. With test times in the order of a few milliseconds, conventional force balances cannot be applied here. The technique has been applied in a number of shock tunnels utilizing models up to approximately 300 mm in length and looking at external aerodynamics. In the present study the technique is applied using a complex 1.5 m long hypersonic integrated supersonic combustion ramjet (scramjet) engine consisting of intake, combustor and thrust nozzle. For scramjet engines the design objective is a combustor with efficient mixing and combustion within the shortest possible length, but still robust enough to operate in various operational conditions. In the framework of the EU co-funded project LAPCAT II, a M=7.4 scramjet powered small scale flight experiment (SSFE) configuration was designed. Since free jet testing of the complete combustion flow path is a mandatory step within the design roadmap of future engines, ground based testing of the SSFE engine was conducted in the High Enthalpy Shock Tunnel Gottingen (HEG) of the German Aerospace Center, DLR. This type of facility allows duplication of flight conditions in excess of M=8. Here tests were performed simulating Mach 7.4 flight conditions in approximately 28 km altitude. The numerically predicted thrust of the engine could be confirmed in HEG utilizing optical tracking of the free flight wind tunnel model. Combining these experimental results with computed aerodynamic data of the complete SSFE showed that for a selected flight condition a positive aero propulsive balance of the complete configuration could be achieved.