Abstract
Axisymmetric simulations of a liquid rocket engine are performed using a delayed detached-eddy-simulation (DDES) turbulence model with the Compressible Flamelet Progress Variable (CFPV) combustion model. Three different pressure instability domains are simulated: completely unstable, semi-stable, and fully stable. The different instability domains are found by varying the combustion chamber and oxidizer post length. Laminar flamelet solutions with a detailed chemical mechanism are examined. The β probability density function (PDF) for the mixture fraction and Dirac δ PDF for both the pressure and the progress variable are used. A coupling mechanism between the volumetric Heat Release Rate (HRR) and the pressure in an unstable cycle is demonstrated. Local extinction and reignition are investigated for all the instability domains using the full S-curve approach. A monotonic decrease in the amount of local extinctions and reignitions occurs when pressure oscillation amplitude becomes smaller. The flame index is used to distinguish between the premixed and non-premixed burning mode in different stability domains. An additional simulation of the unstable pressure oscillation case using only the stable flamelet burning branch of the S-curve is performed. Better agreement with experiments in terms of pressure oscillation amplitude is found when the full S-curve is used.
Highlights
In recent years, there is an increasing need for computational efficient numerical tools to simulate accurately the combustion dynamics in high-power propulsion engines such as liquid rocket engines, scramjets, and gas turbine engines
In the Eddy Dissipation Model [3], the reaction source terms are calculated based on turbulence quantities and different constants
The total Heat Release Rate (HRR) rate for n number of species is defined as n
Summary
There is an increasing need for computational efficient numerical tools to simulate accurately the combustion dynamics in high-power propulsion engines such as liquid rocket engines, scramjets, and gas turbine engines. In the Thickened Flame Model approach, flames are artificially thickened to be resolved on numerical grids by multiplying diffusion and dividing reaction rates by a thickening factor [4, 5] Another approach is the Linear Eddy Mixing (LEM) model [6, 7], in which the relevant advectiondiffusion-reaction couplings are resolved using a low-dimensional representation of turbulent advection. In these models, usage of any realistic detailed chemical mechanisms involving tens of species and hundreds of reactions present a difficult challenge due to the enormous computational cost. Because of the high dimensionality of its argument with Monte-Carlo simulations of at least 30-50 notional particles in a cell, the PDF simulations are usually very computationally expensive even with a simple chemistry model [8]
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