Identification of Whistling Ability of a Single Hole Orifice From an Incompressible Flow Simulation

2011 ◽  
Author(s):  
Romain Lacombe ◽  
Pierre Moussou ◽  
Yves Aure´gan
Keyword(s):  
Mach Number ◽  
Acoustic Waves ◽  
Flow Simulation ◽  
Navier Stokes ◽  
Resonant Condition ◽  
Average Flow Velocity ◽  
Fluid Behavior ◽  
The Difference ◽  
Physical Features ◽  
Lock In

Pure tone noise from orifices in pipe result from vortex shedding with lock-in. Acoustic amplification at the orifice is coupled to resonant condition to create self-sustained oscillations. One key feature of this phenomenon is hence the ability of an orifice to amplify acoustic waves in a given range of frequencies. Here a numerical investigation of the linear response of an orifice is undertaken, with the support of experimental data for validation. The study deals with a sharp edge orifice. Its diameter equals to 0.015 m and its thickness to 0.005 m. The pipe diameter is 0.030 m. An air flow with a Mach number 0.026 and a Reynolds number 18000 in the main pipe is present. At such a low Mach number, the fluid behavior can reasonably be described as locally incompressible. The incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved with the help of a finite volume fluid mechanics software. The orifice is submitted to an average flow velocity, with superimposed small harmonic perturbations. The harmonic response of the orifice is the difference between the upstream and downstream pressures, and a straightforward calculation brings out the acoustic impedance of the orifice. Comparison with experiments shows that the main physical features of the whistling phenomenon are reasonably reproduced.

FLOWS OF VISCOUS COMPRESSIBLE FLUIDS UNDER STRONG STRATIFICATION: INCOMPRESSIBLE LIMITS FOR LONG-RANGE POTENTIAL FORCES

2011 ◽  
Vol 21 (01) ◽  
pp. 7-27 ◽  
Author(s):  
EDUARD FEIREISL
Keyword(s):  
Mach Number ◽  
Acoustic Waves ◽  
Stokes System ◽  
Hybrid Methods ◽  
Singular Limit ◽  
Acoustic Energy ◽  
Compressible Fluids ◽  
Navier Stokes ◽  
Whole Space ◽  
Rage Theorem

We study the singular limit of the compressible Navier–Stokes system in the whole space ℝ3, where the Mach number and Froude number are proportional to a small parameter ε → 0. The central issue is the local decay of the acoustic energy proved by means of the RAGE theorem. The result is quite general and the proposed approach can be applied to a large variety of problems that concern propagation of acoustic waves in compressible fluids. In particular, the method can be used for showing stability of various numerical schemes based on the so-called hybrid methods.

Axisymmetric acoustic scattering by vortices

2002 ◽  
Vol 473 ◽  
pp. 275-294 ◽  
Author(s):  
Y. HATTORI ◽  
STEFAN G. LLEWELLYN SMITH
Keyword(s):  
Mach Number ◽  
Born Approximation ◽  
Acoustic Waves ◽  
Three Dimensional ◽  
Acoustic Scattering ◽  
Order Effects ◽  
Incoming Wave ◽  
Spherical Vortex ◽  
The Difference ◽  
Higher Order Effects

The scattering of acoustic waves by compact three-dimensional axisymmetric vortices is studied using direct numerical simulation in the case where the incoming wave is aligned with the symmetry axis and the direction of propagation of the vortices. The cases of scattering by Hill’s spherical vortex and Gaussian vortex rings are examined, and results are compared with predictions obtained by matched asymptotic expansions and the Born approximation. Good agreement is obtained for long waves, with the Born approximation usually giving better predictions, especially as the difference in scale between vortex and incoming waves decreases and as the Mach number of the flow increases. An improved version of the Born approximation which takes into account higher-order effects in Mach number gives the best agreement.

scholarly journals STABILITY WITH RESPECT TO DOMAIN OF THE LOW MACH NUMBER LIMIT OF COMPRESSIBLE VISCOUS FLUIDS

2013 ◽  
Vol 23 (13) ◽  
pp. 2465-2493 ◽  
Author(s):  
EDUARD FEIREISL ◽  
TRYGVE KARPER ◽  
ONDŘEJ KREML ◽  
JAN STEBEL
Keyword(s):  
Mach Number ◽  
Acoustic Waves ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Compact Set ◽  
Solenoidal Vector ◽  
Navier Stokes Equations ◽  
Low Mach Number Limit ◽  
Neumann Laplacian ◽  
Solenoidal Vector Field

We study the asymptotic limit of solutions to the barotropic Navier–Stokes system, when the Mach number is proportional to a small parameter ε → 0 and the fluid is confined to an exterior spatial domain Ωε that may vary with ε. As ε → 0, it is shown that the fluid density becomes constant while the velocity converges to a solenoidal vector field satisfying the incompressible Navier–Stokes equations on a limit domain. The velocities approach the limit strongly (a.a.) on any compact set, uniformly with respect to a certain class of domains. The proof is based on spectral analysis of the associated wave propagator (Neumann Laplacian) governing the motion of acoustic waves.

scholarly journals Physics of Vibrating Airfoils at Low Reduced Frequency

2013 ◽  
Author(s):  
Almudena Vega ◽  
Roque Corral
Keyword(s):  
Mach Number ◽  
Acoustic Waves ◽  
Unsteady Aerodynamics ◽  
Low Pressure ◽  
Travelling Wave ◽  
Navier Stokes ◽  
Influence Coefficient ◽  
Reduced Frequency ◽  
Influence Coefficients ◽  
Key Aspects

The unsteady aerodynamics of low pressure turbine vibrating airfoils in flap mode is studied in detail using a frequency domain linearized Navier-Stokes solver. Both the travelling-wave and influence coefficient formulations of the problem are used to highlight key aspects of the physics and understand different trends such as the effect of reduced frequency and Mach number. The study is focused in the low-reduced frequency regime which is of paramount relevance for the design of aeronautical low-pressure turbines and compressors. It is concluded that the effect of the Mach number on the unsteady pressure phase can be neglected in first approximation and that the unsteadiness of the vibrating and adjacent airfoils is driven by vortex shedding mechanisms. Finally a simple model to estimate the work-per-cycle as a function of the reduced frequency and Mach Number is provided. The edge-wise and torsion modes are presented in less detail but it is shown that acoustic waves are essential to explain its behaviour. The non-dimensional work-per-cycle of the edge-wise mode shows a large dependence with the Mach number while in the torsion mode a large number of airfoils is needed to reconstruct the work-per-cycle departing from the influence coefficients.

scholarly journals Numerical simulation and experimental validation of cavitating flow in a multi-hole diesel fuel injector

2021 ◽  
pp. 146808742199863
Author(s):  
Aishvarya Kumar ◽  
Ali Ghobadian ◽  
Jamshid Nouri
Keyword(s):  
Computational Cost ◽  
Cavitating Flow ◽  
Field Analysis ◽  
Navier Stokes ◽  
Fuel Injector ◽  
Fluid Behavior ◽  
Flow Field Analysis ◽  
Charged Couple Device ◽  
Biodiesel Fuels ◽  
High Level

This study assesses the predictive capability of the ZGB (Zwart-Gerber-Belamri) cavitation model with the RANS (Reynolds Averaged Navier-Stokes), the realizable k-epsilon turbulence model, and compressibility of gas/liquid models for cavitation simulation in a multi-hole fuel injector at different cavitation numbers (CN) for diesel and biodiesel fuels. The prediction results were assessed quantitatively by comparison of predicted velocity profiles with those of measured LDV (Laser Doppler Velocimetry) data. Subsequently, predictions were assessed qualitatively by visual comparison of the predicted void fraction with experimental CCD (Charged Couple Device) recorded images. Both comparisons showed that the model could predict fluid behavior in such a condition with a high level of confidence. Additionally, flow field analysis of numerical results showed the formation of vortices in the injector sac volume. The analysis showed two main types of vortex structures formed. The first kind appeared connecting two adjacent holes and is known as “hole-to-hole” connecting vortices. The second type structure appeared as double “counter-rotating” vortices emerging from the needle wall and entering the injector hole facing it. The use of RANS proved to save significant computational cost and time in predicting the cavitating flow with good accuracy.

Computed Effects of Rotor-Induced Swirl on Brush Seal Performance—Part 2: Bristle Force Analysis

1996 ◽  
Vol 118 (4) ◽  
pp. 920-926 ◽  
Author(s):  
M. C. Sharatchandra ◽  
D. L. Rhode
Keyword(s):  
Inclination Angle ◽  
Flow Direction ◽  
Flow Simulation ◽  
Companion Paper ◽  
Navier Stokes ◽  
Brush Seal ◽  
Swirl Flows ◽  
Lift Off ◽  
Square Configuration ◽  
Periodic Module

This paper analytically investigates the aerodynamic bristle force distributions in brush seals used in aircraft gas turbine engines. These forces are responsible for the onset of bristle tip lift-off from the rotor surface which significantly affects brush seal performance. In order to provide an enhanced understanding of the mechanisms governing the bristle force distributions, a full Navier-Stokes flow simulation is performed in a streamwise periodic module of bristles corresponding to the staggered square configuration. As is the case with a companion paper (Sharatchandra and Rhode, 1996), this study has the novel feature of considering the combined effects of axial (leakage) and tangential (swirl) flows. Specifically, the effects of intra-bristle spacing and bristle inclination angle are explored. The results indicate that the lifting bristle force increases with reduced intra-bristle spacing and increased inclination angle. It was also observed that increases in the axial or tangential flow rates increased the force component in the normal as well as the flow direction.

Standing acoustic waves in a low Mach number shear flow

AIAA Journal ◽  
1992 ◽  
Vol 30 (7) ◽  
pp. 1708-1715 ◽  
Author(s):  
Meng Wang ◽  
David R. Kassoy
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Acoustic Waves ◽  
Low Mach Number

Analysis of Aeroacoustic Phenomena in Centrifugal Compressors Using a Lattice Boltzmann Flow Simulation Approach

2020 ◽  
Author(s):  
Rahul Phogat ◽  
Néstor González Díez ◽  
Jan Smeulers ◽  
Damiano Casalino ◽  
Francesco Avallone
Keyword(s):  
Lattice Boltzmann ◽  
Acoustic Waves ◽  
Dynamic Pressure ◽  
Flow Simulation ◽  
Acoustic Mode ◽  
Secondary Flows ◽  
Pressure Loading ◽  
Compressor Cascade ◽  
High Fatigue ◽  
Return Channel

Abstract Impeller rotation, vortex shedding, secondary flows or a combination of these phenomena can lead to the generation of acoustic waves in the compressor cascade causing dynamic pressure loading on the impeller. When the eigenfrequency and eigenmode shape of the acoustic mode match with the structural ones of the impeller, high fatigue stresses and vibrations occur, which can lead to structural failure. It is well known that cavities enclosing shrouded impellers may strongly amplify the acoustic excitation of the impeller by means of Tyler-Sofrin modes; however, little knowledge is available about the physics of flow-induced noise and resonance mechanisms. In this research, a Lattice Boltzmann Method based approach is employed to predict the origin and amplitude of pressure loading responsible for the strong impeller trailing edge vibrations measured in experiments. The results reveal that this is caused by the acoustic mode generated from the interaction of upstream vane wakes with the impeller that is reflected by the return channel vanes. This research highlights the importance of accounting for aeroacoustic mechanisms in the design of centrifugal compressor stages and paves the way towards the numerical assessment of unsteady flow and resonance phenomena.

Modal Decomposition and Linear Modeling of Swirl Fluctuations in the Mixing Section of a Model Combustor Based on PIV Data

2021 ◽  
Author(s):  
Jens Satria Müller ◽  
Finn Lückoff ◽  
Thomas Ludwig Kaiser ◽  
Christian Oliver Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Acoustic Waves ◽  
Stokes Equations ◽  
Flow Instability ◽  
Theoretical Work ◽  
Navier Stokes ◽  
Inertial Waves ◽  
Linear Modeling ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Flow Response

Abstract In order to determine the flame transfer function of a combustion system only based on isothermal flow field data, three governing mechanisms have been identified which need to be modeled: swirl fluctuations, equivalence fluctuations and velocity fluctuations excited by planar acoustic waves. This study focuses on the generation and propagation of swirl fluctuations downstream of a radial swirl combustor under isothermal conditions. Swirl fluctuations are generated experimentally by imposing acoustic perturbations. Time-resolved longitudinal and crosswise PIV measurements are conducted inside the mixing tube and combustion chamber to quantify the evolution of the swirl fluctuations. The measured flow response is decomposed using spectral proper orthogonal decomposition to unravel the contributions of different dynamical modes. In addition a resolvent analysis is conducted based on the linearized Navier-Stokes equations to reveal the intrinsically most amplified flow structures. Both, the data-driven and analytic approach, show that inertial waves are indeed present in the flow response and an inherent flow instability downstream of the swirler, which confirms the recent theoretical work of Albayrak et al. (Journal of Fluid Mechanics, 879). However, the contribution of these inertial waves to the total swirl fluctuations turns out to be very small. This is suggested to be due to the very structured forcing at the swirler and the amplification of shear-driven modes which are expected to be much more influential for this type of swirler. Overall, this work confirms the presence of inertial waves in highly turbulent swirl combustors and evaluates its relevance for industry-related configurations. It further outlines a methodology to analyze and predict their characteristics based on mean fields only, which is applicable for complex geometries of industrial relevance.

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