Yasser Mahmoudi

Hydrodynamic Instabilities in Gaseous Detonations: Comparison of Euler, Navier–Stokes, and Large-Eddy Simulation

A large-eddy simulation is conducted to investigate the transient structure of an unstable detonation wave in two dimensions and the evolution of intrinsic hydrodynamic instabilities. The dependency of the detonation structure on the grid resolution is investigated, and the structures obtained by large-eddy simulation are compared with the predictions from solving the Euler and Navier–Stokes equations directly. The results indicate that to predict irregular detonation structures in agreement with experimental observations the vorticity generation and dissipation in small scale structures should be taken into account. Thus, large-eddy simulation with high grid resolution is required. In a low grid resolution scenario, in which numerical diffusion dominates, the structures obtained by solving the Euler or Navier–Stokes equations and large-eddy simulation are qualitatively similar. When high grid resolution is employed, the detonation structures obtained by solving the Euler or Navier–Stokes equations directly are roughly similar yet equally in disagreement with the experimental results. For high grid resolution, only the large-eddy simulation predicts detonation substructures correctly, a fact that is attributed to the increased dissipation provided by the subgrid scale model. Specific to the investigated configuration, major differences are observed in the occurrence of unreacted gas pockets in the high-resolution Euler and Navier–Stokes computations, which appear to be fully combusted when large-eddy simulation is employed.

Temperature fields in a channel partially filled with a porous material under local thermal non-equilibrium condition – An exact solution:

This work examines analytically the forced convection in a channel partially filled with a porous material and subjected to constant wall heat flux. The Darcy–Brinkman–Forchheimer model is used to represent the fluid transport through the porous material. The local thermal non-equilibrium, two-equation model is further employed as the solid and fluid heat transport equations. Two fundamental models (models A and B) represent the thermal boundary conditions at the interface between the porous medium and the clear region. The governing equations of the problem are manipulated, and for each interface model, exact solutions, for the solid and fluid temperature fields, are developed. These solutions incorporate the porous material thickness, Biot number, fluid to solid thermal conductivity ratio and Darcy number as parameters. The results can be readily used to validate numerical simulations. They are, further, applicable to the analysis of enhanced heat transfer, using porous materials, in heat exchangers.

Triple Point Collision and Hot Spots in Detonations with Regular Structure

In the present work, the details of a regular structure detonation are studied using very high-resolution two-dimensional numerical simulations. It is found that more than 300 points per half reaction length are required to resolve properly the nature of the transverse waves and the structure configuration during the collision and reflection processes of a triple point and its associated transverse wave with the channel walls. The detonation structure is found to be a double-Mach configuration, while it changes to a single-Mach configuration shortly before collision of the triple points with the wall. During the reflection, the shear layer becomes detached from the front and recedes from it, producing a pocket of partly unburned gas. After reflection, the structure is a single-Mach configuration, while it changes to a double-Mach configuration after some time. Shortly before collision, a hot spot, containing partly burned gases, is formed behind the incident wave at the vicinity of the wall. This hot spot ultimately burns by mixing of burned and unburned gases due to the existence of small-scale vortices produced by Kelvin–Helmholtz instability along the detached shear layer.

Combustion Noise Analysis of Open Flames Using Incompressible LES

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. The potentials of using large eddy simulation (LES) with low Mach number (incompressible) formulation to predict combustion noise from premixed flames in open environment are investigated. The spatio-temporal variation of heat release rate obtained from LES of these flames are used to compute the far field sound pressure level and its power spectral density for various equivalence ratios and turbulence levels. Computational results are compared to measurements to assess the efficacy of the LES approach and the agreement is found to be very good. The advantages and limitations of this LES approach are identified and discussed.

Prediction of combustion noise in a model combustor using a network model and a lnse approach

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Low-Order Modelling of Combustion Noise in an Aero-Engine: The Effect of Entropy Dispersion

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Acoustic and entropy waves in nozzles in combustion noise framework

A low-order model is presented to study the propagation and interaction of acoustic and entropic perturbations through a convergent–divergent nozzle. The calculations deal with choked, unchoked, as...