2,403 research outputs found
The Impacts of Three Flamelet Burning Regimes in Nonlinear Combustion Dynamics
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 Probability Density Function (PDF)
for the mixture fraction and Dirac PDF for both the pressure and the
progress variable are used. A coupling mechanism between the Heat Release Rate
(HRR) and the pressure in an unstable cycle is demonstrated. Local extinction
and reignition is 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.Comment: 25 pages, 12 figures. Submitted to Combustion and Flame for a Special
Issu
Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models
The present paper deals with the numerical study of high pressure LOx/H2 or
LOx/hydrocarbon combustion for propulsion systems. The present research effort
is driven by the continued interest in achieving low cost, reliable access to
space and more recently, by the renewed interest in hypersonic transportation
systems capable of reducing time-to-destination. Moreover, combustion at high
pressure has been assumed as a key issue to achieve better propulsive
performance and lower environmental impact, as long as the replacement of
hydrogen with a hydrocarbon, to reduce the costs related to ground operations
and increase flexibility. The current work provides a model for the numerical
simulation of high- pressure turbulent combustion employing detailed chemistry
description, embedded in a RANS equations solver with a Low Reynolds number
k-omega turbulence model. The model used to study such a combustion phenomenon
is an extension of the standard flamelet-progress-variable (FPV) turbulent
combustion model combined with a Reynolds Averaged Navier-Stokes equation
Solver (RANS). In the FPV model, all of the thermo-chemical quantities are
evaluated by evolving the mixture fraction Z and a progress variable C. When
using a turbulence model in conjunction with FPV model, a probability density
function (PDF) is required to evaluate statistical averages of chemical
quantities. The choice of such PDF must be a compromise between computational
costs and accuracy level. State- of-the-art FPV models are built presuming the
functional shape of the joint PDF of Z and C in order to evaluate
Favre-averages of thermodynamic quantities. The model here proposed evaluates
the most probable joint distribution of Z and C without any assumption on their
behavior.Comment: presented at AIAA Scitech 201
Numerical framework for transcritical real-fluid reacting flow simulations using the flamelet progress variable approach
An extension to the classical FPV model is developed for transcritical
real-fluid combustion simulations in the context of finite volume, fully
compressible, explicit solvers. A double-flux model is developed for
transcritical flows to eliminate the spurious pressure oscillations. A hybrid
scheme with entropy-stable flux correction is formulated to robustly represent
large density ratios. The thermodynamics for ideal-gas values is modeled by a
linearized specific heat ratio model. Parameters needed for the cubic EoS are
pre-tabulated for the evaluation of departure functions and a quadratic
expression is used to recover the attraction parameter. The novelty of the
proposed approach lies in the ability to account for pressure and temperature
variations from the baseline table. Cryogenic LOX/GH2 mixing and reacting cases
are performed to demonstrate the capability of the proposed approach in
multidimensional simulations. The proposed combustion model and numerical
schemes are directly applicable for LES simulations of real applications under
transcritical conditions.Comment: 55th AIAA Aerospace Sciences Meeting, Dallas, T
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