Computational Analysis of Tonal Noise Generated High-Bypass Ratio Fan Stage

2005 ◽  
Author(s):  
Aleksey M. Sipatov ◽  
Michail V. Usanin ◽  
Valery G. Avgustinovich ◽  
Natalia O. Chuhlantseva
Keyword(s):  
Pressure Distribution ◽  
Acoustic Analysis ◽  
Stokes Equations ◽  
Near Field ◽  
Hybrid Approach ◽  
Leading Edge ◽  
Navier Stokes ◽  
Far Field ◽  
Unsteady Pressure ◽  
Acoustic Contribution

The paper shows the procedure of estimating different fan stage geometries from the point of the fan stage aerodynamic and acoustic efficiency by using CFX v.5.6 gas dynamics software. Two different fan stages were examined. The acoustic analysis was made based on unsteady pressure distribution along exit guide vanes. The unsteady pressure distribution was determined from 3-D calculations of rotor-stator interactions. An improved approach is suggested to estimate acoustic sources with the leading edge geometry considered. Three various grid models were analyzed to estimate the grid discretization influence on computational results. The hybrid approach was used to evaluate the acoustic contribution of fan stage rotor–stator interaction to a turbo-jet engine total noise level on first harmonic in a far field. This approach consists of three steps. The first step includes the solving of Navier-Stokes equations in fan stage, the second step includes the solving of linearized Euler’s equations (LEE) in a near field and, then, the third covers the calculation of Ffowcs Williams–Hawkings (FWH) integral in a far field. The first step marked the effect of strong attenuation of acoustics modes in the fan passage. The results of calculations in the far field were compared with experiment data.

ANALYSIS OF A HETEROGENEOUS DOMAIN DECOMPOSITION FOR COMPRESSIBLE VISCOUS FLOW

2001 ◽  
Vol 11 (04) ◽  
pp. 565-599 ◽  
Author(s):  
CRISTIAN A. COCLICI ◽  
WOLFGANG L. WENDLAND
Keyword(s):  
Domain Decomposition ◽  
Stokes Equations ◽  
Domain Decomposition Method ◽  
Near Field ◽  
Outer Region ◽  
Navier Stokes ◽  
Far Field ◽  
Computational Domain ◽  
Linearized Euler Equations ◽  
Naca0012 Airfoil

We analyze a nonoverlapping domain decomposition method for the treatment of two-dimensional compressible viscous flows around airfoils. Since at some distance to the given profile the inertial forces are strongly dominant, there the viscosity effects are neglected and the flow is assumed to be inviscid. Accordingly, we consider a decomposition of the original flow field into a bounded computational domain (near field) and a complementary outer region (far field). The compressible Navier–Stokes equations are used close to the profile and are coupled with the linearized Euler equations in the far field by appropriate transmission conditions, according to the physical properties and the mathematical type of the corresponding partial differential equations. We present some results of flow around the NACA0012 airfoil and develop an a posteriori analysis of the approximate solution, showing that conservation of mass, momentum and energy are asymptotically attained with the linear model in the far field.

scholarly journals Sound generation in a mixing layer

1997 ◽  
Vol 330 ◽  
pp. 375-409 ◽  
Author(s):  
TIM COLONIUS ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Acoustic Field ◽  
Stokes Equations ◽  
Near Field ◽  
Mixing Layer ◽  
Navier Stokes ◽  
Far Field ◽  
Source Terms ◽  
Acoustic Analogy ◽  
Navier Stokes Equations ◽  
Acoustic Sources

The sound generated by vortex pairing in a two-dimensional compressible mixing layer is investigated. Direct numerical simulations (DNS) of the Navier–Stokes equations are used to compute both the near-field region and a portion of the acoustic field. The acoustic analogy due to Lilley (1974) is also solved with acoustic sources determined from the near-field data of the DNS. It is shown that several commonly made simplifications to the acoustic sources can lead to erroneous predictions for the acoustic field. Predictions based on the quadrupole form of the source terms derived by Goldstein (1976a, 1984) are in excellent agreement with the acoustic field from the DNS. However, despite the low Mach number of the flow, the acoustic far field generated by the vortex pairings cannot be described by considering compact quadrupole sources. The acoustic sources have the form of modulated wave packets and the acoustic far field is described by a superdirective model (Crighton & Huerre 1990). The presence of flow–acoustic interactions in the computed source terms causes the acoustic field predicted by the acoustic analogy to be very sensitive to small changes in the description of the source.

Direct computation of the sound generated by vortex pairing in an axisymmetric jet

1999 ◽  
Vol 383 ◽  
pp. 113-142 ◽  
Author(s):  
BRIAN E. MITCHELL ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Mach Number ◽  
Stokes Equations ◽  
Near Field ◽  
Prediction Method ◽  
Axial Direction ◽  
Navier Stokes ◽  
Far Field ◽  
Source Terms ◽  
Vortex Pairing ◽  
Field Sound

The sound generated by vortex pairing in axisymmetric jets is determined by direct solution of the compressible Navier–Stokes equations on a computational grid that includes both the near field and a portion of the acoustic far field. At low Mach number, the far-field sound has distinct angles of extinction in the range of 60°–70° from the jet's downstream axis which can be understood by analogy to axisymmetric, compact quadrupoles. As the Mach number is increased, the far-field sound takes on a superdirective character with the dominant sound directed at shallow angles to the jet's downstream axis. The directly computed sound is compared to predictions obtained from Lighthill's equation and the Kirchhoff surface method. These predictions are in good agreement with the directly computed data. The Lighthill source terms have a large spatial distribution in the axial direction necessitating the introduction of a model to describe the source terms in the region downstream of the last vortex pairing. The axial non-compactness of the quadrupole sources must be adequately treated in the prediction method.

A Parametric Study of Air-Pumping Phenomenon in Tire Grooves Using Computational Fluid Dynamics

2016 ◽  
Author(s):  
Prashanta Gautam ◽  
Yousof Azizi ◽  
Abhilash J. Chandy
Keyword(s):  
Computational Model ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Near Field ◽  
Hybrid Approach ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Analytical Prediction ◽  
Tire Noise ◽  
Tire Rotation

The tire/road interaction process results in generation of noise, which is transmitted and audible in the inside and outside of the car. In the recent years, the structural-borne noise in a tire has been extensively studied. However, very few studies have been conducted on air-borne noise. Various studies and indoor experimental measurements suggest that among all air-borne tire noise mechanisms, air-pumping mechanisms, i.e. rapid displacement of air near the tire/road contact patch, is the dominant source of noise for certain tires and operating conditions. This research focuses on studying air-pumping mechanisms and uses a previously developed computational model to predict air-borne noise generated using a hybrid approach. The basis of the hybrid approach is a direct prediction of near-field solution using compressible Navier-Stokes equations with turbulence modeling, combined with an analytical prediction of far-field acoustics using an acoustic model. Only the near-field acoustic characteristics are discussed in this paper. The tire rotation and groove deformations at the tire/road contact is modeled through mesh motion and prescribed deformation functions, thereby circumventing the need for coupling with a structural solver for fluid-structure interactions. The capability of the developed computational model in estimating the tire noise is shown and the effects of varying different parameters such as tire speed and geometry on the evolution of the estimated responses at various near-field receiver locations are studied.

Analytical and Numerical Investigations on the Aeroacoustical Oscillation of Flow Past the Cavity

2015 ◽  
Author(s):  
Weidong Shao ◽  
Jun Li
Keyword(s):  
Stokes Equations ◽  
Near Field ◽  
Navier Stokes ◽  
Far Field ◽  
Navier Stokes Equations ◽  
Flow Past ◽  
Tonal Frequency ◽  
Number Flow ◽  
Unsteady Characteristics ◽  
Flow Flux

Noise radiated by aeroacoustical oscillation of low Mach number flow past a two-dimensional cavity has been investigated analytically and numerically using electro-acoustical analogy and a hybrid scheme combining CFD with an implementation of the porous Ffowcs Williams-Hawkings equation. The noise generation mechanism is illustrated and the interaction between flow and cavity as well as key factors of resonant frequency is discussed. The 2D compressible unsteady Reynolds averaged Navier-Stokes equations (URANS) are solved to obtain near field acoustic source and unsteady characteristics of cavity flow. A buffer domain is exerted along all external boundaries to suppress boundary wave reflection. Computed tonal frequency and amplitude of pressure oscillations demonstrate good agreement with previous computational simulations and experiments. The influences of the length and shape of the neck and porous inserts on the noise radiated to the far field are also investigated. The 3D far field numerical results show that at a certain incoming flow velocity and shear layer thickness the frequency of the dominant oscillation increases with the length of the neck and the magnitude in the downstream far field is 8dB greater than that in the upstream far field. The increasing chamfer decreases the resonance frequency and changes the effective streamwise opening length resulting in significant differences in acoustic pressure fluctuation. The porous inserts on the floor of the cavity reduce the mass flow flux through the cavity neck and accordingly suppress the amplitude of dominant oscillation. The preliminary simulations reveal promising methods for sound radiation control.

Influences of Recess Geometry and Restrictor Dimension on Flow Patterns and Pressure Distribution of Hydrostatic Bearings

2007 ◽  
Author(s):  
Cheng-Hsien Chen ◽  
Yuan Kang ◽  
Yeon-Pun Chang ◽  
De-Xing Peng ◽  
Ding-Wen Yang
Keyword(s):  
Pressure Distribution ◽  
Stokes Equations ◽  
Flow Patterns ◽  
Lubricant Film ◽  
Navier Stokes ◽  
Width Ratio ◽  
Navier Stokes Equations ◽  
Hydrostatic Bearing ◽  
Lubricant Flow ◽  
Land Width

This paper studies the influences of recess geometry and restrictor dimensions on the flow patterns and pressure distribution of lubricant film, which are coupled effects of hybrid characteristics of a hydrostatic bearing. The lubricant flow is described by using the Navier-Stokes equations. The Galerkin weighted residual finite element method is applied to determine the lubricant velocities and pressure in the bearing clearance. The numerical simulations will evaluate the effects of the land-width ratio and restriction parameter as well as the influence of modified Reynolds number and the jet-strength coefficient on the flow patterns in the recess and pressure distribution in lubricant film. On the basis of the simulation drawn from this study, the simulated results are expected to help engineers make better use of the design of hydrostatic bearing and its restrictors.

Numerical investigation of an anti-icing method on airfoil based on the NSDBD plasma actuator

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Junjie Niu ◽  
Weimin Sang ◽  
Feng Zhou ◽  
Dong Li
Keyword(s):  
Phenomenological Model ◽  
Stokes Equations ◽  
Pulse Repetition Frequency ◽  
Leading Edge ◽  
Pulse Frequency ◽  
Plasma Actuator ◽  
Navier Stokes ◽  
Peak Voltage ◽  
Content Type ◽  
Naca0012 Airfoil

Purpose This paper aims to investigate the anti-icing performance of the nanosecond dielectric barrier discharge (NSDBD) plasma actuator. Design/methodology/approach With the Lagrangian approach and the Messinger model, two different ice shapes known as rime and glaze icing are predicted. The air heating in the boundary layer over a flat plate has been simulated using a phenomenological model of the NSDBD plasma. The NSDBD plasma actuators are planted in the leading edge anti-icing area of NACA0012 airfoil. Combining the unsteady Reynolds-averaged Navier–Stokes equations and the phenomenological model, the flow field around the airfoil is simulated and the effects of the peak voltage, the pulse repetition frequency and the direction arrangement of the NSDBD on anti-icing performance are numerically investigated, respectively. Findings The agreement between the numerical results and the experimental data indicates that the present method is accurate. The results show that there is hot air covering the anti-icing area. The increase of the peak voltage and pulse frequency improves the anti-icing performance, and the direction arrangement of NSDBD also influences the anti-icing performance. Originality/value A numerical strategy is developed combining the icing algorithm with the phenomenological model. The effects of three parameters of NSDBD on anti-icing performance are discussed. The predicted results show that the anti-icing method is effective and may be helpful for the design of the anti-icing system of the unmanned aerial vehicle.

Leading Edge Film Cooling: Computations and Experiments Including Density Effects

1996 ◽  
Author(s):  
Pingfan He ◽  
Dragos Licu ◽  
Martha Salcudean ◽  
Ian S. Gartshore
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Stokes Equations ◽  
Leading Edge ◽  
Variable Density ◽  
Navier Stokes ◽  
Cooling Effectiveness ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

The effect of varying coolant density on film cooling effectiveness for a turbine blade-model was numerically investigated and compared with experimental data. This model had a semi-circular leading edge with four rows of laterally-inclined film cooling orifices positioned symmetrically about the stagnation line. A curvilinear coordinate-based CFD code was developed and used for the numerical investigation. The code used a domain segmentation strategy in conjunction with general curvilinear grids to model the complex blade configuration. A multigrid method was used to accelerate the convergence rate. The time-averaged, variable-density, Navier-Stokes equations together with the energy or scalar equation were solved. Turbulence closure was attained by the standard k–ε model with a near-wall k model. Either air or CO2 was used as coolant in three cases of injection through single rows and alternatively staggered double raws of holes. Two different blowing rates were investigated in each case and compared with experimental data. The experimental results were obtained using a wind tunnel model, and the mass/heat analogy was used to determine the film cooling effectiveness. The higher density of the carbon dioxide coolant (approximately 1.5 times the density of air) in the isothermal mass injection experiments, was used to simulate the effects of injection of a colder air in the corresponding adiabatic heat transfer situation. Good agreement between calculated and measured film cooling effectiveness was found for low blowing ratio M ≤ 0.5 and the effect of density was not significant. At higher blowing ratio M > 1 the calculations consistently overpredict the measured values of film cooling effectiveness.

Numerical Simulation of Clocking Effect on Wake Transportation and Interaction in a 1.5-Stage Axial Turbine

2010 ◽  
Author(s):  
Wei Li ◽  
Hua Ouyang ◽  
Zhao-hui Du
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Leading Edge ◽  
Navier Stokes ◽  
Maximum Efficiency ◽  
Suction Surface ◽  
Navier Stokes Equations ◽  
Pressure Surface ◽  
Turbine Efficiency ◽  
Small Influence

To give insight into the clocking effect and its influence on the wake transportation and its interaction, the unsteady three-dimensional flow through a 1.5-stage axial low pressure turbine is simulated numerically using a density-correction based, Reynolds-Averaged Navier-Stokes equations commercial CFD code. The 2nd stator clocking is applied over ten equal tangential positions. The results show that the harmonic blade number ratio is an important factor affecting the clocking effect. The clocking effect has a very small influence on the turbine efficiency in this investigation. The efficiency difference between the maximum and minimum configuration is nearly 0.1%. The maximum efficiency can be achieved when the 1st stator wake enters the 2nd stator passage near blade suction surface and its adjacent wake passes through the 2nd stator passage close to blade pressure surface. The minimum efficiency appears if the 1st stator wake impinges upon the leading edge of the 2nd stator and its adjacent wake of the 1st stator passed through the mid-channel in the 2nd stator.

WAVELET-BASED POSTPROCESSING OF JET LES DATA FOR ACOUSTIC FAR-FIELD EXTRAPOLATIONS

2013 ◽  
Vol 21 (04) ◽  
pp. 1350017
Author(s):  
RAMIN KAVIANI ◽  
VAHID ESFAHANIAN ◽  
MOHAMMAD EBRAHIMI
Keyword(s):  
Large Scale ◽  
Stokes Equations ◽  
Near Field ◽  
Flow Simulation ◽  
Computational Time ◽  
Jet Flows ◽  
Small Scale ◽  
Frequency Noise ◽  
Far Field ◽  
Noise Sources

The affordable grid resolutions in conventional large-eddy simulations (LESs) of high Reynolds jet flows are unable to capture the sound generated by fluid motions near and beyond the grid cut-off scale. As a result, the frequency spectrum of the extrapolated sound field is artificially truncated at high frequencies. In this paper, a new method is proposed to account for the high frequency noise sources beyond the resolution of a compressible flow simulation. The large-scale turbulent structures as dominant radiators of sound are captured in LES, satisfying filtered Navier–Stokes equations, while for small-scale turbulence, a Kolmogorov's turbulence spectrum is imposed. The latter is performed via a wavelet-based extrapolation to add randomly generated small-scale noise sources to the LES near-field data. Further, the vorticity and instability waves are filtered out via a passive wavelet-based masking and the whole spectrum of filtered data are captured on a Ffowcs-Williams/Hawkings (FW-H) surface surrounding the near-field region and are projected to acoustic far-field. The algorithm can be implemented as a separate postprocessing stage and it is observed that the computational time is considerably reduced utilizing a hybrid of many-core and multi-core framework, i.e. MPI-CUDA programming. The comparison of the results obtained from this procedure and those from experiments for high subsonic and transonic jets, shows that the far-field noise spectrum agree well up to 2 times of the grid cut-off frequency.

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