Near-field Pressure Fluctuations Research Articles

Aeroacoustic characteristics of a strut-braced high-lift device

The aerodynamic and aeroacoustic performance of a strut-based high-lift device were evaluated and demonstrated for six different strut models. The primary objective of the study was to investigate the impact of strut modifications on reducing noise levels. The aerodynamic characteristics are presented with the aid of surface pressure distribution on the airfoil that remained consistent across all the tested configurations. The aeroacoustic results are presented as the near-field surface pressure fluctuations and far-field noise measurements to attain a profound comprehension of the noise generation mechanism. Although the Albatros strut exhibited the greatest reduction in tonal noise, the directivity pattern and the overall sound pressure level of the radiated noise demonstrated that the medium height strut configuration can achieve noise reduction of up to 8 dB. The near-field unsteady surface pressure measurements are suggestive of harmonic oscillations. The coherence studies carried out have shown a decrease in the tonal coherence for the small height strut configuration while the velocity field measurements performed in the wake of the high-lift device show no significant variation in flow patterns between different strut configurations.

Control of separated flow at low Reynolds number around NACA0012 airfoil by boundary layer suction

The separated flow at low Reynolds number around the NACA0012 airfoil is numerically studied by large-eddy simulation. Strategies of boundary layer suction to control flow separation are investigated. A method of using two-zone suctions, near the leading edge and near the trailing edge, are calculated. Based on verification with direct numerical simulation (DNS) and experimental data, the results of the lift and the drag, the vortices, and the strength of near-field pressure fluctuations, are checked. The results show that the two-zone suctions can supress flow transition and separation, thereby increase the lift and reduce the drag. The shedding of vortices is weakened, and the near-field pressure fluctuations are attenuated. For comparison with the two-zone suctions, the strategies of suction near the leading edge only and suction near the trailing edge only are also studied. It is found that suction near the leading edge only may suppress transition and delay separation when the suction zone is large enough, but the flow property deteriorates due to shedding vortices in the wake. The suction near the trailing edge only may improve the flow performance by reducing the size of the vortices in the rear section of the airfoil and in the wake region, but it has little effect on the separation bubble and transition.

Experimental studies on pressure drag and aerodynamic noise of cylinder with porous coatings

Previous numerical studies hold inconsistent viewpoints of the porous coating on a circular cylinder reducing or increasing drag, and the present experimental study aims to clarify this argument. Additionally, a common viewpoint is that the porous coatings can suppress both the near-field wall pressure fluctuations and far-field acoustic pressure, but optimal parameters of the porous materials are still unclear. In this paper, the experimental studies reveal effects of three parameters, i.e., incoming flow velocity, pores per inch, and thickness of metal foams, on the pressure drag, wall pressure fluctuations, and associated noise level.

Perturbation-based active flow control in overexpanded to underexpanded supersonic rectangular twin jets

The effects of perturbation-based active flow control on supersonic rectangular twin jets (SRTJ) over a wide range of nozzle pressure ratios (NPR = 2.77 to 6.7, corresponding to fully expanded Mach numbers Mj = 1.3 to 1.9) were investigated. The aspect ratio and design Mach number for the bi-conic, converging-diverging nozzles were 2 and 1.5, respectively. The flow and acoustic fields of SRTJ are known to couple, often generating high near-field (NF) pressure fluctuations and elevated far-field (FF) noise levels. Large-scale structures (LSS), or equivalently instability waves or wave packets, are responsible for mixing noise, broadband shock-associated noise, screech and coupling. The primary objective of this research was to manipulate the development of LSS in this complex flow to better understand and mitigate their effects. The organization and passage frequency of the LSS were altered by excitation of instabilities over a wide range of frequencies and modes. Key findings include: (1) the screech mode of each jet was flapping along its minor axis; (2) the jets coupled, out-of-phase primarily in overexpanded cases and in-phase primarily in underexpanded cases, along the minor axis of the SRTJ; (3) coupling has significant effects on the NF pressure fluctuations, but only minor effect on the FF noise; (4) standing waves were observed only on the minor axis plane of the SRTJ; (5) altering or suppressing coupling can significantly reduce NF pressure fluctuations; (6) two high-frequency excitation methods proved effective in reducing the FF noise; and (7) nonlinear interactions between the screech tones and excitation input were observed in controlled cases in which screech was only partially suppressed.

Numerical investigation on aerodynamic noise of flow past a cylinder with different spanwise lengths

A numerical investigation is conducted on aerodynamic noise of flow past a circular cylinder with different spanwise lengths (0.5πD, πD, 2πD, and 4πD) at Re = 10 000, where D is the diameter of the cylinder. The near-field pressure and velocity fields are predicted through Large Eddy Simulation, and then, the acoustic analogy is used to obtain the far-field noise. The results show good agreements for both the near and far field with the data from in-house experiments and the literature. Though the spanwise length has limited influence on the power spectral density of the near-field velocity and pressure fluctuations at different spanwise locations, substantial differences are observed for the spanwise pressure coherence and near-wake structures. The 0.5πD case shows primarily two-dimensional flow features immediately behind the cylinder compared to the other three cases, resulting in the overprediction of the spanwise pressure coherence, which has strong implications for the far-field noise prediction. With the spanwise length correction, the differences in overall noise magnitudes of the different cases diminish. Nevertheless, the 2πD and 4πD cases better capture the first and second harmonics of the vortex shedding and its associated directivities than the other two cases, showing the importance of sufficient spanwise lengths in predicting noise from flow past a cylinder.

Active control of coupling and its effect on near-field pressure fluctuations in supersonic rectangular twin jets

Supersonic rectangular twin jets (SRTJ) are of interest for current and future generations of tactical aircraft. However, the adverse effects of screech-loop coupling have previously been documented to significantly increase the near-field (NF) pressure fluctuations. These high-amplitude pressure fluctuations have the potential to fatigue and damage nearby aft components of the aircraft. Previous studies have documented that the NF pressure fluctuation level depends on the coupling of the jets: in-phase coupling along the twin jets’ minor axes produces stronger NF pressure fluctuations than that of out-of-phase coupling. The objective of this work is to further investigate the effects of coupling modes on NF pressure fluctuations in SRTJ and to mitigate the adverse effects of coupling using active flow control. Localized arc filament plasma actuators are employed to alter the SRTJs’ coupling mode by leveraging natural flow instabilities with minimal power input. A NF microphone array is used for simultaneous coupling and NF pressure fluctuation measurements. Schlieren imaging and spectral proper orthogonal decomposition are used to assess the effects of control on the flow field. The effect of excitation at various frequencies and actuation patterns on coupling and NF pressure fluctuations in different flow regimes are explored and discussed.

Influence of orifice thickness and chamfer on broadband noise in a water circuit

An incompressible large-eddy simulation (LES) is used to predict broadband noise generation by an orifice in a water circuit. Flow conditions are chosen in order to avoid cavitation. The model’s results are compared to measured wall pressure fluctuations for three orifices: a thin sharp-square-edge orifice, a thick sharp-square-edge orifice and a thick narrower orifice with an upstream chamfer. Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulations (LES) fail to reproduce the steady-flow drag coefficient of the thick sharp-edge orifice and of the upstream-chamfered orifice. Large differences are found in the steady-flow drag coefficient of different samples of the thick orifice. An edge-tone like instability is observed in the near-field pressure fluctuations of one of the thick sharp-square-edge orifices, which does not appear in the other samples and is suppressed by the upstream chamfer. However, there are only minor differences in far-field radiated sound for these thick sharp-edged orifices. A plane-wave model with acoustic source from the LES predicts the power spectral density (PSD) of the acoustic pressures within a factor 3. At low Strouhal numbers (based on the orifice diameter and the cross-sectional averaged velocity in the orifice) the thin orifice behaves similarly to the thicker strongly chamfered orifices, with thin central cylindrical section. At higher Strouhal numbers the measured and predicted acoustic-pressure fluctuations due to these orifices are two orders of magnitude lower than those of thick orifices with sharp square edges. As orifices are used for the control of the flow distribution through complex water-cooling networks, the good results for thick chamfered narrow orifices call for a further study to find shapes that minimize the sound production at constant static pressure drop.

Hydrodynamic and acoustic pressure fluctuations in water pipes due to an orifice: Comparison of measurements with Large Eddy Simulations

The present article investigates the turbulent wall pressure fluctuations due to flow through single-hole sharp-square-edged orifices (opening area ratios of 11%, 20% and 31%) in a water-filled pipe by means of measurements and incompressible Large Eddy Simulations (LES) for opening area ratios of 20% and 31%. The orifice plate thickness was half the orifice diameter. The static pressure measurements and simulations show that the vena-contracta factors of the orifices are dependent on Reynolds numbers, which is due to the finite thickness of the orifices. These LES simulations provide a good prediction of the near-field hydrodynamic wall pressure fluctuations, which dominate up to the first three pipe diameters downstream of the orifice. Upstream and far downstream wall pressure fluctuations are dominated by acoustic pressure fluctuations. The source of the radiated sound field was estimated from the surface integral of the fluctuations across the orifice in the LES. The sound field was calculated by implementing the sound source in a one dimensional acoustic model of the test section. The power spectrum density (PSD) of the wall pressure fluctuations for pipe Reynolds numbers varying from 4000 to 10000 collapsed when presented in dimensionless form, which uses the dynamic pressure in the orifice as reference pressure and the ratio of cross-sectional averaged orifice velocity and orifice diameter as characteristic frequency. In the inertial range of the turbulence a global decay of the pressure PSD and of the sound source show a power of the Strouhal number between −113 and −2.8. For higher frequencies the pressure fluctuations were dominated by acoustic resonances. For wider orifices the magnitude of these acoustic pressure fluctuations is predicted within a factor two by the acoustic model. For the narrowest orifice (opening ratio of 11%) the measured PSD of pressure fluctuations displays sharp peaks due to self-sustained oscillations (whistling). A simple power law of the sound source is not accurate due to the unstable hydrodynamic modes related to orifice thickness. However, using the simple model for the sound source the acoustic model predicts the acoustic pressure fluctuations reasonably well for all orifices. At low frequency one observes a peak in the PSD hydrodynamic wall-pressure fluctuations at one pipe diameter downstream of the orifice. It is probably due to an acoustically silent “edge-tone-like” sinusoidal self-sustained motion of the jet.

A Wavelet-Based Time-Frequency Analysis on the Supersonic Jet Noise Features with Chevrons

A detailed investigation of the statistical properties of the near-field pressure fluctuations induced by an under-expanded jet, by varying the nozzle exit shapes has been presented. Experiments using different convergent Chevron nozzles were carried out in the anechoic chamber at the University of Bristol to assess the importance of the Chevron shape on the near pressure field emitted by a single stream under-expanded jet. Measurements were carried out through an axial microphone array traversed radially to various positions for jet in an under-expanded condition at Mach number M = 1.3. The intermittent behavior is investigated considering the standard statistical indicators and a wavelet-based conditional approach, including the phase angle. The intermittent degree of various features related to different scales, such as Screech tones and broadband shock associate noise were estimated. A series of recently developed wavelet-based tools were assessed as a viable approach to investigate the noise emitted by under-expanded jets.

A numerical study on near-field pressure fluctuations of symmetrical and anti-symmetrical flapping modes of twin-jet using a high-resolution shock-capturing scheme

Screeching supersonic jets appears at off-design operating conditions and is perceived as an intense tonal noise. In a twin nozzle configuration, mutual interactions between the two jet plumes may occur with various coupling modes developing depending on the operating conditions and lateral distance between the jets. The investigation of the detailed flow behaviors and near-field pressure fluctuations with relevance to the twin jets system, the analysis of the developed instabilities, will enhance understanding of fundamental features associated with jets located close to each other.In the present study, the single jet is considered first to assess the large eddy simulation (LES) approach used and the near-field pressure fluctuation predictions. Based on the validated solver, twin jets are simulated. Two different twin-nozzle configurations having different separation distance or nozzle-to-nozzle centerline spacing are scrutinized for the same Mach number of 1.358. Notably, the twin jets are screeching by the coupling mode for both set-ups; however, the case of closer inter-nozzle distance presents a symmetrical dominant flapping mode, while the other case shows an anti-symmetrical flapping mode. The strength of the pressure fluctuation at the fundamental frequency changes depending on the location of the observer point (upstream or downstream) and the reference plane (twin-jet and normal to the twin-jet plane). The screech tones of the two cases, observable in the upstream region, are significantly different in the normal to the twin-jet plane direction because of the phase difference of fluctuating pressure. However, the first harmonic component remains strong, regardless of the flapping mode. It is also observed that, at the fundamental frequency, the amplitude of the pressure fluctuation at downstream locations is found to be strong in the normal to the twin-jet plane when the symmetrical flapping mode occurs. This feature is also observed in the twin-jet plane in the case of the opposite mode. By analyzing the developed vertical structures and performing correlation analyses of pressure fluctuations along jet shear layers, the periodicity of the flow in the downstream region with relevance to the fundamental frequency is revealed.

Acoustic and flow characteristics of an airfoil fitted with morphed trailing edges

An experimental study of a simple NACA 0012 airfoil fitted with two different flap profiles was carried out to characterize their aerodynamic and aeroacoustic performance. The airfoil with a flap deflection angle of β = 10° was tested for a wide range of angles of attack at a chord-based Reynolds number of Rec=2.6×105. The aerodynamic lift and drag measurements show improved lift-to-drag performance for the morphed flap airfoil compared to the hinged flap airfoil at low angles of attack. Surface flow visualization and boundary layer measurements on the suction surface of the flap show delayed separation for the morphed flap airfoil. Higher-order moments of the wall pressure fluctuations were also used to observe the flow separation over the flap. Additionally, Particle Image Velocimetry was also used to study the flow over the flap and at the airfoil wake. Flow measurements showed that the downstream wake development could be significantly influenced by the flap camber. The mean velocity contours at the wake showed increased wake velocity deficit and turbulent kinetic energy for the morphed flap airfoil. The turbulent kinetic energy results displayed a characteristic double peak behavior which was also the dominant characteristics of the streamwise Reynolds shear stress component. Near-field unsteady surface pressure fluctuations and far-field noise measurements show reduced point spectra and noise levels for morphed flap configuration at low angles of attack but considerably increased noise levels at high angles of attack compared to hinged flap configuration.

Numerical investigation of the effects of gas-liquid ratio on the spray characteristics of liquid-centered swirl coaxial injectors

We investigate the effects of gas-liquid ratio (GLR) on the spray and atomization process of a liquid-centered swirl coaxial injector using the coupled level-set and volume of fluid (CLSVOF) method. The flow field, gas-liquid interaction, and breakup of liquid film during adaptive mesh refinement are evaluated and analyzed. The results show that, with the increase of GLR, the atomization process becomes dominated successively by the instability of the liquid film, strong gas-liquid interaction and spray self-pulsation. Moreover, more droplets are found near the center of the spray cone while the spray angle decreases. The inclined surface waves on the liquid film may be formed owing to Rayleigh-Taylor instability. When GLR is relatively large, holes are produced and break up on the liquid film due to the high velocity of the gas. Then, the gas-liquid interaction pushes small droplets towards the center of the spray cone, while large droplets and ligaments distribute on the periphery of the spray. With even larger GLRs, self-pulsation occurs, which is found to determine the flow structures inside the spray cone and to generate, shed and dissipate vortices periodically. Furthermore, when self-pulsation occurs, the near-field pressure and mass flow rate fluctuations increase rapidly.

Aerodynamic and aeroacoustic performance of high-lift airfoil fitted with slat cove fillers

Experimental measurements were carried out to assess the aerodynamic and aeroacoustic performance of an MDA 30P30N airfoil fitted with two different types of slat cove fillers. The aerodynamic results are presented for lift and drag measurements and mean surface pressure measurements, while the aeroacoustic results are presented for the near-field surface pressure fluctuations and far-field noise measurement. The flow measurement results show that there is no significant difference in the aerodynamic lift and drag between the tested cases, however, the slat cove filler configurations exhibit a much better lift-to-drag performance. The pressure coefficient results show that the use of slat cove fillers lead to a slight decrease in the suction peak over the main-element of the airfoil. In order to better understand the flow-field and the noise generation mechanism of the airfoil with slat cove fillers, simultaneous near-field and far-field noise measurements were carried out. The result shows that the use of the slat cove filler can generally lead to a significant reduction of the broadband noise and eliminate the characteristic tonal noise generated by the slat. The directivity pattern and the overall sound pressure level of the radiated noise have shown that a significant noise reduction can be achieved with the applications of the slat cove fillers. The multiple tonal phenomena generated by the slat were also analyzed using the continuous wavelet transform method and higher order spectral analysis methods.

Effect of a Chevron Nozzle on Noise Radiation from a Compressible Jet

The effect of a chevron on a radiated (acoustic) component of near-field pressure fluctuations in a high-speed compressible jet is experimentally investigated for a nozzle exit Mach number of 0.8. The main focus in the present experimental study is to examine the effect of a chevron on noise sources, their location in the jet flowfield, and the noise radiation pattern in the far-field through simultaneous measurement of near-field and far-field pressure fluctuations using a cross-correlation technique. The formation of lobes in the mixing layer close to the chevron nozzle exit alters the near-field and far-field noise characteristics as compared to the base nozzle. The overall sound pressure level closer to the chevron nozzle exit increases, whereas downstream of the potential core, it reduces in comparison with the base nozzle. Furthermore, the position of the near-field/far-field cross-correlation coefficient peak suggests that the interaction of chevrons with the jet flow moves the dominant noise source upstream and closer to the nozzle exit. The chevron nozzle disintegrates large-scale flow structures, thereby reducing the noise levels radiating at a lower polar angle in the far-field. The near-field/far-field cross-correlations suggest that an acoustic component of the near-field pressure fluctuations, propagating from the jet to the higher polar angles in the far-field, is generated by fine-scale turbulent flow structures in the region close to the nozzle exit, and the chevron nozzle is found to strongly support this mechanism. An increase in the noise levels closer to the nozzle exit in the near-field and at a higher polar angle in the far-field are due to high-frequency noise sources generated by the chevron nozzle.

Analysis of Coherent Structures in an Under-Expanded Supersonic Impinging Jet Using Spectral Proper Orthogonal Decomposition (SPOD)

The spatiotemporal dynamics of the coherent structures in an under-expanded supersonic impinging jet are studied using a spectral proper orthogonal decomposition technique. For this analysis, a large eddy simulation of an under-expanded supersonic impinging jet at a pressure ratio of 3.4 and a stand-off distance of 2 jet diameters at a Reynolds number of 50,000 is performed. The mean flow fields illustrate some striking features of this flow, such as an oblique shock, a stand-off shock, a Mach disk, and a recirculation bubble. The spectral proper orthogonal decomposition method is applied to time-resolved three-dimensional flow fields. The accumulative energy of modes within each azimuthal mode number reveals that the first three azimuthal modes contain most of the energy of the flow. The spectra of these azimuthal modes show that the flow exhibits a low-ranked behaviour with discrete frequencies at the optimal symmetric azimuthal mode while other two azimuthal modes have negligible contributions in this behaviour. Three peaks are observed in the spectra of the optimal symmetric azimuthal mode. The spatial fields of the streamwise velocity and pressure of these peaks show that the complex structures are consequences of the under-expansion, Mach disk, and the impingement. Strong hydrodynamic instabilities exist in the shear layer of the jet in the optimal azimuthal mode at each of these dominant frequencies. High-amplitude acoustic waves are also present in the near-field of the jet. These acoustic waves are strong at the nozzle lip, suggesting that a feedback loop linking these two processes exists for dominant frequencies in the optimal mode. High cross-spectrum density of near-field pressure fluctuations and streamwise velocity fluctuations near the nozzle lip at these frequencies confirms the hydro-acoustic coupling, which is necessary to close the feedback loop.

Experimental study of turbulent-jet wave packets and their acoustic efficiency

This paper details the statistical and time-resolved analysis of the relationship between the near-field pressure fluctuations of unforced, subsonic free jets (0.4 ≤ M ≤ 0.6) and their far-field sound emissions. Near-field and far-field microphone measurements were taken on a conical array close to the jets and an azimuthal ring at 20∘ to the jet axis, respectively. Recent velocity and pressure measurements indicate the presence of linear wave packets in the near field by closely matching predictions from the linear homogenous parabolized stability equations, but the agreement breaks down both beyond the end of the potential core and when considering higher order statistical moments, such as the two-point coherence. Proper orthogonal decomposition (POD), interpreted in terms of inhomogeneous linear models using the resolvent framework allows us to understand these discrepancies. A new technique is developed for projecting time-domain pressure measurements onto a statistically obtained POD basis, yielding the time-resolved activity of each POD mode and its correlation with the far field. A single POD mode, interpreted as an optimal high-gain structure that arises due to turbulent forcing, captures the salient near-field–far-field correlation signature; further, the signatures of the next two modes, understood as suboptimally forced structures, suggest that these POD modes represent higher order, acoustically important near-field behavior. An existing Green's-function-based technique is used to make far-field predictions, and results are interpreted in terms of POD/resolvent modes, indicating the acoustic importance of this higher order behavior. The technique is extended to provide time-domain far-field predictions.

Dynamics of Closely Spaced Supersonic Jets

A twin-jet configuration is composed of two jets placed in closed proximity to each other. Previous works on such configurations have been mostly experimental in nature. The aim of this work is to computationally analyze a twin-jet configuration and identify the impact of plume interactions on various aspects, such as shear-layer characteristics, coherent structures, mixing, and the near acoustic field. A large-eddy simulation (LES)-based approach is employed to study a Mach 1.23 circular twin-jet configuration with an internozzle spacing of two jet diameters. In agreement with the established literature, results indicate a dominant helical mode on both the jet plumes. In the internozzle region, mean velocity profiles indicate the formation of a secondary flow, which extends a significant influence on the shear layers in its proximity. However, this impact is confined to small azimuthal angles and, as a result, many of the potential core properties are almost similar to those of a single jet at identical flow conditions. Along the plane containing the jet centers, analysis of the near-field pressure fluctuations reveals that the twin jet exhibits suppressed levels relative to a single jet. This is ascribed to twin-jet plume bending along with reduced outer shear-layer spreading rate.

Exploring Physics and Control of Twin Supersonic Circular Jets

The closely spaced twin-jet configuration often seen in military aircraft is distinct from the single jet in both the flowfield and acoustic field. The twin-jet plumes interact with each other weakly or strongly, depending upon the distance between the two jets, the jet operating flow regime, and the Mach number. In the current study, the interaction mechanisms and coupling of a supersonic twin jet exhausting from biconical converging–diverging nozzles with a design Mach number of 1.23 at a separation distance of two nozzle exit diameters are investigated using near-field pressure measurements and phase-locked flow visualization. Across a series of jet operating Mach numbers, the twin-jet plumes feature three major jet azimuthal modes: axisymmetric, helical, and flapping. The jet flapping mode is strongly augmented in the twin-jet configuration compared to the single-jet case. Along the twin-jet plane, which is also the plane of the jet flapping direction, jet plumes with coherent flow structures are observed to move up and down. Because of the nature of the jet flapping motion, the near-field pressure fluctuations are markedly amplified at low Strouhal numbers, particularly along the twin-jet plane for further downstream locations where the coherent structures are developed and large. Localized arc filament plasma actuators are implemented as an active flow control tool on both nozzles, just upstream of nozzle exit, to explore the coupling mechanisms. The results show that decoupling and coupling of twin-jet plumes can both be achieved, depending on the jet operating condition and the excitation parameters employed.

Wave-Packet Representation of Shock-Cell Noise for a Single Round Jet

From a viewpoint analogous to the wave-packet model, the shock-cell-noise model developed by Harper-Bourne and Fisher (“The Noise from Shock Waves in Supersonic Jets,” AGARD Rept. CP-131, 1974) is directly evaluated using unsteady pressure fields computed with a large-eddy simulation. Continuum two-point correlation functions of near-field pressure fluctuations in a single round jet are projected to acoustic fields as a boundary-value problem, and the expression is transformed into a discrete representation equivalent to the Harper-Bourne and Fisher model. In this process, the two-point correlation is reconstructed using the snapshot proper orthogonal decomposition technique in the frequency domain (namely, the cross-spectral correlation). Accordingly, hydrodynamic and acoustic fields associated with shock-cell noise are visualized for each azimuthal mode. From explicit correspondence between the Harper-Bourne and Fisher model and the cross-spectral correlation function, the validity of the model is analyzed in terms of the active shock-cell sites, the correlation length, the phase velocity, and the contributions from azimuthal modes as a function of the Strouhal number. Many aspects of the Harper-Bourne and Fisher model, such as the discrete nature and the correlation length scale, are justified; on the other hand, the importance of some missing aspects, especially the azimuthal content and the harmonic wave-number components, is found at a Strouhal number of approximately two or higher.

A Computational Fluid Dynamics Model for Investigating Air-Pumping Mechanisms in Air-Borne Tire Noise

ABSTRACT The reduction in power train noise over the past decade has led to an increased focus in reducing tire/road noise, largely due to the environmental concerns related to road traffic noise in industrial countries. Computational fluid dynamic (CFD) simulations conducted using ANSYS FLUENT are presented here with the objective of understanding air-pumping noise-generation mechanisms due to tire/road interaction. The CFD model employs a large eddy simulation turbulence modeling approach, in which the filtered compressible Navier-Stokes equations are solved to obtain temporally and spatially accurate near-field pressure fluctuations for a two-dimensional (2D) tire geometry with (1) one groove and (2) two grooves. In addition, the Ffowcs-Williams and Hawkings (FW-H) acoustic model is used to predict far-field acoustics. The deformation of the grooves, as the tire rotates, is represented by prescribed sidewall movements. Consequently, the solution to the numerical problem is obtained through a single process, thereby enabling the prediction of small-scale air pumping, horn effect, and far-field acoustics in a single simulation. The acoustic characteristics associated with air pumping are studied through spectral analysis tools, and comparisons show that the additional groove on the horn geometry alters the spectral characteristics of air pumping. Validation of the model is conducted through qualitative and quantitative comparisons with previous studies. These simulations are intended to provide a deeper understanding about the small-scale noise generation as well as the near-field and far-field acoustics, thereby paving the way for the automotive manufacturer to compare a variety of air-related tire noise characteristics without spending time and money for vehicle pass-by tests.