A Conceptional Approach for the Prediction of Thermoacoustic Stability in Rocket Engines

Abstract

A methodology to predict thermoacoustic stability in rocket engines is presented. It is based on a divide and conquer principle. The central elements, consisting of the combustion chamber and the nozzle are calculated together directly by a hybrid approach using an extended version of the DLR's acoustic solver PIANO. Beside these central elements, the different components affecting the overall thermoacoustic stability are simulated separately and their properties are lumped into an adequate mathematical description, which is then integrated into PIANO. Each component is analyzed and optimized in its individual environment to reduce the complexity of the interaction processes, which govern thermoacoustics. The challenging step however is the incorporation of all components into a complete stability analysis and thereby keep the computational cost within reasonable limits to make this approach attractive for industrial purposes. In this report the fundamental approach is explained as well as the different components are described by means of their relevance for thermoacoustics and used modelling approaches are shown. Finally the strengths of the approach are confronted with its disadvantages. Especially its realizability and future prospects are discussed.

Influence of atomization quality modulation on flame dynamics in a hypergolic rocket engine

“…In the engine, the MMH flow is axially injected through 12 radially oriented slits with an outer radius of R o, M ¼ 0:26 and disintegrates downstream of the slits into droplets. In the numerical computations, however, the MMH droplets are injected with a homogeneously distributed velocity u Inj, M through the surface of several truncated cones with an opening angle of 5 and with the base being located at the slits. The circular base diameter of the cones corresponds to the slit width.…”

“…This allows the numerical computation of flame dynamics on the basis of single injector numerical modeling, 2 which finally must be cast in feedback models for the wave propagation code to provide access to the evaluation of rocket engine combustion stability. [2][3][4][5]10 The description of acoustic propagation within the entire thrust system is then based on linearized equations, which reduce computational efforts substantially. Stability ratings based on linear equations, however, state only the linear stability, i.e.…”

“…Most of them model the thermoacoustic feedback provided by flame dynamics separately from the wave propagation in the combustion chamber. [2][3][4][5][6][7][8][9] The separated determination of flame dynamics and wave propagation is necessary, since state of the art computational fluid dynamics (CFD) tools are not capable of providing fully discretized simulations of realistic rocket engine configurations including a high number of injectors over acoustically relevant time spans. Single injector investigations, however, allow for detailed studies on combustion processes and parameter variations are possible.…”

A comparison of time and frequency domain descriptions of high frequency acoustics in rocket engines with focus on dome coupling

“…Against this background, a CFD/CAA (Computational Aeroacoustics) approach has been developed at the Lehrstuhl für Thermodynamik, Technische Universität München, see [3][4][5][6]. The essential ingredient to reduce computational effort is to exploit separation of small scale effects such as turbulent combustion from considerable bigger scales of acoustic propagation.…”

Linear stability assessment of a cryogenic rocket engine

“…Such methods are commonly referred to as computational fluid dynamics/computational aeroacoustics (CFD/CAA) hybrid approaches. [9][10][11][12][13] CFD/CAA methodologies for the assessment of combustion stability are also used for gas turbines. [14][15][16] The capability of assessing a realistic rocket engine type in terms of combustion stability is shown in Schulze et al 17 However, the recently held third modeling workshop on combustion instabilities a in the framework of the French-German research initiative REST evidently showed that a predictive level is not yet reached by any type of simulation.…”