Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

Resolved simulations of the sound-induced flow through a circular orifice with a 0.99 mm diameter are examined. The orifice is backed by a hexagonal cavity and is a local model for acoustic liners commonly used for aeroengine noise reduction. The simulation data identify the role the orifice wall boundary layers play in determining the orifice discharge coefficient which, in time-domain models, is an important indicator of nonlinearity. It is observed that when the liner behaviour is not well described by linear models, the orifice boundary layers contain secondary vorticity generated from its separation from the corner on the high-pressure side of the orifice. Quantitative comparisons of the simulation-predicted impedance match available data for incident sound of 130 dB amplitude at frequencies from 1.5 to 3.0 kHz. At amplitudes of 140–160 dB, the simulation impedance is in agreement with analytical predictions when using simulation-measured quantities, including the discharge coefficient and root-mean-square velocity through the orifice, although no experimental data for this liner exist at these conditions. The simulation data are used to develop two time-domain models for the acoustic impedance wherein the velocity profile through the orifice is modelled as the product of the fluid velocity and a presumed radial shape, . The models perform well, predicting the in-orifice velocity and pressure, and the impedance, except for the most nonlinear cases where it is seen that the assumed shape can affect the backplate pressure predictions. These results suggest that future time-domain models that take the velocity profile into account, by modelling the boundary layer thickness and assuming a velocity profile shape, may be successful in predicting the nonlinear response of the liner.

Numerical investigation and modelling of acoustically excited flow through a circular orifice backed by a hexagonal cavity

Direct numerical simulations are used to study the interaction of a cavity-backed circular orifice with grazing laminar and turbulent boundary layers and incident sound waves. The flow conditions and geometry are representative of single degree-of-freedom acoustic liners applied in the inlet and exhaust ducts of aircraft engines and are the same as those from experiments conducted at NASA Langley. The simulations identify the fluid mechanics of how the sound field and state of the grazing boundary layer impact the in-orifice flow and suggest a simple flow analogy that enables scaling estimates. From the scaling estimates the simulations are then used to develop reduced-order models for the in-orifice flow and a time-domain impedance model is constructed. The liner is found to increase drag at all conditions studied by an amount that increases with the incident sound pressure amplitude.

Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

Numerical and experimental investigation of the acoustic damping effect of single-layer perforated liners with joint bias-grazing flow

Dynamics and mechanisms of pressure, heat release rate, and fuel spray coupling during intermittent thermoacoustic oscillations in a model aeronautical combustor at elevated pressure

An adjoint-based method for liner impedance eduction: Validation and numerical investigation

https://hal.archives-ouvertes.fr/hal-01870188/document

Long Elastic Open Neck Acoustic Resonator for low frequency absorption

The aim of this work is to study the role of the liquid phase in the thermo-acoustic coupling which subsequently leads to combustion instabilities. Experimental investigations were performed on an actual multipoint spray injector geometry used in real aeronautical combustors. A test bench was specifically designed with continuously changeable acoustics conditions; which allows obtaining a stable or an unstable flame for identical flow conditions. Different laser-based visualization techniques were used to analyze the kerosene spray (both liquid and vapor phases) and the heat released from the flame. A phase-averaged data processing of the Planar Laser-Induced Fluorescence (PLIF) images reveals the complex unsteady behavior of the liquid phase and its coupling with pressure fluctuations in the chamber and the heat released from the flame. The origins of the spray fluctuations are also analyzed. Nomenclature = surface of the control system boundary, m 2 = volume of the control system, m 3 = heat capacity ratio = characteristic time, s dA = surface integration variable, 1 m 2 dt = time integration variable, 1 s dV = volume integration variable, 1 m 3 D REF = reference diameter F = Flame Describing Function FSP = Fuel Split Parameter GER = Global Equivalent Ratio I = light intensity over camera dynamics, # counts IEL = Inner Exhaust Length, mm J = momentum ratio air m  = air mass flow rate, g/s P f m ,  = fuel mass flow rate on the pilot system, g/s MP f m ,  = fuel mass flow rate on the multipoint system, g/s p' = acoustic pressure, Pa p = averaged pressure, Pa q' = unsteady heat release, W/m 3 Ra = local Rayleigh index T = instability cycle period, s T air = air inlet temperature, K u' = acoustic velocity, m/s

/pdf/liquid-fuel-behavior-in-an-aeronautical-injector-submitted-3bdwq3psy8.pdf

Liquid-Fuel Behavior in an Aeronautical Injector Submitted to Thermoacoustic Instabilities

This paper describes a new liner impedance eduction technique. The two-dimensional Linearized Euler Equations are solved in the frequency domain with a Discontinuous Galerkin formulation. The objective function which is minimized for impedance eduction is based on two-dimensional acoustic velocity elds measured by Laser Doppler Anemometry. The optimization scheme is based on direct and adjoint equations, which allows easily the

Liner impedance eduction technique based on velocity fields

https://acoustique.ec-lyon.fr/publi/betgen_applacoust12.pdf

Frank Simon

Papers

An adjoint-based method for liner impedance eduction: Validation and numerical investigation

Long Elastic Open Neck Acoustic Resonator for low frequency absorption

Liquid-Fuel Behavior in an Aeronautical Injector Submitted to Thermoacoustic Instabilities

Liner impedance eduction technique based on velocity fields

Implementation and non-intrusive characterization of a hybrid active-passive liner with grazing flow