Chaitanya Paruchuri

University of Southampton · Institute of Sound and Vibration Research (ISVR)

Cyclonic separator systems with tangential inlets are frequently used in industrial applications to provide centrifugal forces for efficient separation and after the separation the purified fluid exits upwards through exhaust ducts. A very high levels of tonal noise has been observed when the cyclonic air flow change direction from a higher volume...

This paper presents a predominately experimental investigation of the reduction of noise from shrouded propellers by using Over-Tip-Rotor (OTR) liners. Experimental far-field noise data has been obtained for SDOF and grooved metal foam liners installed upstream of the propeller, in an OTR position, and downstream of the propeller. A bellmouth intak...

This short paper presents a preliminary experimental investigation of the influence of unequal diameters in co-axial contra-rotating rotors at hover conditions on their acoustic and aerodynamic performance. A parametric study is conducted to investigate the sensitivity of the radiated noise and performance metrics to the axial separation distance f...

Propeller operation in close proximity to a strut involves interactions from multiple sources, significantly contributing to noise generation. This study aims to reduce this interaction noise by employing a porous strut as a noise mitigation strategy. The paper presents experimental measurements of far-field noise for three types of rods: two solid...

In this study, we investigate the noise produced by a propeller installed in a pusher configuration in close proximity to a wing. Experiments are conducted in a state-of-the-art anechoic wind tunnel to observe the impact of both static and in-flight conditions on overall noise generation. We found that as the separation distance increases, the inte...

This paper investigates the aeroacoustic characteristics of 2-bladed propellers during the edgewise forward flight and descent phases of eVTOL aircraft through experimentally and numerically. Acoustic signatures were analyzed across various advance ratios and tilt angles (±𝛽), ranging from +10◦ during climb to -30◦ during descent. It was found that...

The application of a porous coating to a bluff body, such as a cylinder, is an efficient passive flow control method and has applications in wind, aerospace, and civil engineering. Despite its effectiveness in reducing vortex-shedding processes and the associated noise-generating mechanisms, there exists a trade-off in terms of the generation of hi...

Among the various noise sources related to duct fans, the noise generated by the interaction of the tip leakage flow with the blade geometric singularities is one of the least understood noise sources. Our past experimental investigations on a stationary aerofoil have highlighted two tip noise sources, localised at the mid-chord and at 75% of the c...

Over-Tip-Rotor (OTR) liners have been investigated over the last decades as a technology to further reduce fan broadband noise in turbofan engines. The suppression of noise with OTR liners is attributed to conventional attenuation of acoustic waves and source modification effects. This paper describes a fundamental experiment to gain a better under...

This study presents a predominantly numerical and theoretical investigation into the balance of tonal and broadband noise due to an isolated propeller in uniform motion. The predicted trends in the balance between tonal and broadband noise radiation with varying blade number and speed of rotation is supported by preliminary experimental measurement...

The application of acoustic liners near/directly over a sound source has gained significant interest for the excess noise reduction achieved with Over-the-Rotor (OTR) liners compared to the conventional liner installations at the intake of an aero-engine. However, the mechanism of noise reduction achieved in the OTR liners is not clearly understood...

Propellers usually operate in non-uniform flow conditions, leading to significant levels of noise generation due to interaction with the leading edges of the propeller blades. Under these flow conditions, the noise generated can be substantially different from the rotor-alone self-noise generated under uniform mean flow conditions. This paper prese...

Acoustic liners are widely used passive noise reduction technology for aero-engine noise control. Traditional acoustic liners installed in an aero-engine are usually modelled as a Helmholtz resonator, an air-filled cavity sandwiched between a perforated plate and an acoustically rigid back sheet. For wavelengths much greater than the liner's geomet...

This work is a fundamental experimental investigation on reducing the noise caused by the interaction of a turbulent stream with an aerofoil by using a Kevlar section downstream of the aerofoil leading edge. It has been shown previously by the authors that the noise radiated by two flat plates in a tandem configuration in a turbulent flow is signif...

This work is a fundamental investigation of the noise radiated by two flat plates in a tandem configuration in a turbulent flow. It is shown that this configuration is capable of significantly reducing turbulence-aerofoil interaction noise at low frequencies. The current study presents far-field noise experimental data and detailed high-resolution...

This paper investigates the measured noise data in the engine intra-stage, between the rotor and the outlet guide vanes (OGV), to predict the dominant broadband (BB) noise source in the fan-stage. Unlike the engine intake and the bypass, the intra-stage is particularly suitable for estimating the relative contribution of the fan and the OGV BB nois...

The modelling of the surface pressure spectrum beneath a turbulent boundary layer near the trailing edge of an aerofoil with bio-inspired surface treatments, called canopies, is investigated. Canopies are simply a cylindrical rods uniformly spaced along the span of the aerofoil. The velocity measurements indicated that the flow at the trailing edge...

The pressure shielding mechanism of bio-inspired surface treatment, called canopies, has been investigated experimentally and applied to reduce trailing edge noise generated by aero-foils. Surface pressure experiments beneath the boundary layer on a flat and aerofoil section show that canopies can attenuate surface pressure in two frequency ranges,...

This experimental works investigate simplistic porous arrangement at the trailing edge on the aerofoil self-noise radiation. The basis of this works is to utilise the trailing edge geometry to facilitate acoustic interference between two sources that are physically displaced in the longitudinal direction. The study investigated two trailing edge co...

This study presents the results of an experimental study of propeller characteristics of Tip Vortex as formed downstream of a 2-bladed 16-inch propeller during hover state. A comprehensive Cross-wire Hot-wire Anemometry measurements were conducted to characterise the propeller’s Tip Vortex in each of the velocity components. Ensemble averaging of t...

Due to the additional noise reduction obtained with Over-the-Rotor (OTR) liners compared to the conventional liners at the intake of an aero-engine, the application of acoustic liners close to or immediately over a sound source has attracted substantial interest. This enhanced noise reduction in OTR liners is attributed primarily to the source modi...

This paper experimentally characterises the flow behavior within the tip gap area of a single-fixed aerofoil by studying the influence of two non-dimensional parameters. The tip leakage flow behaviour has been previously linked to the geometric ratio between the local aerofoil thickness and the tip gap size. To explore this dependency, several aero...

This paper is a predominantly experimental investigation into the noise generation mechanisms of Fixed-wing Vertical TakeOff and Landing (VTOL) propeller-wing configurations. These new aircraft combine the benefits of being able to land vertically in urban areas while being able to fly like conventional propeller-driven aircraft. However, their uni...

This research conducts an experimental investigation of the far-field acoustic properties of propellers with different pitch values. Discussions were held regarding the underlying physical principles and how pitch value affects the noise source mechanism in propellers. The classical propeller Broadband noise model was validated and utilised as an o...

This paper presents an experimental investigation of the influence of propeller design parameters and in-flight effects on the interaction noise of co-axial contra-rotating rotors. A parametric study is performed to investigate the sensitivity of the radiated noise to the axial separation distance for different blade pitch angles and number of blad...

A detailed experimental analysis of the aerodynamic and aeroacoustic properties of flat-plate axial fans with slitted leading edges is performed. The sound emissions of five slitted leading edge designs are measured at a constant rotational speed and at a constant total-to-static pressure rise of the fans. For both cases, the fan blades with slitte...

This paper is a predominantly experimental study into the use of porosity located downstream of an aerofoil leading edge for the reduction of turbulence interaction noise. Locating the porosity downstream of the leading edge has been shown to be beneficial in reducing the aerodynamic performance penalty compared with locating it directly at the lea...

The turbulent wake generated by a rotor interacting with outlet guide vanes (OGVs) is one of the dominant broadband noise sources in a turbofan engine. An accurate representation of the rotor wake turbulence is therefore important for the reliable prediction of the rotor–OGV interaction noise. This paper presents a turbulence synthesis method based...

This paper presents the preliminary experimental investigation of the dominant noise sources from the propeller-wing configuration at hover conditions. A parametric study is performed to investigate the sensitivity of the radiated noise to the axial separation distance z and the offset separation distance d between propeller and wing. This study is...

Propellers usually operate in non-uniform flows, which is expected to modify the behaviour of the emitted noise field. In this framework, an experimental campaign with far-field noise measurements of a two-blade propeller, immersed in a non-uniform flow, has been performed in the anechoic facility at the University of Southampton. A parametric anal...

This paper presents a theoretical and numerical investigation into the broadband (BB) modal analysis in complex swirling flows, typical of the aeroengine interstage. Asymptotic (high-frequency limit) wavenumber distribution approaches, measuring the BB modal amplitudes as a continuous distribution over the normalised modal axial wavenumber (ζ) , ha...

In this paper, two surface treatments have been investigated experimentally for reducing trailing edge noise generated by an aerofoil. The aerofoil surface treatments include a Finlet rail supported by rods (called canopies) and walls (called Finlet fences). The surface treatments were applied near the trailing edge of the NACA0012 aerofoil. Far-fi...

This paper considers the modal axial group velocity and its application to broadband (BB) acoustic mode detection in ducted swirling flows, typical of the aeroengine interstage. The normalised modal axial group velocity (ϑ_mn, normalised by the sound speed c) has so far been an analytical construct in duct acoustics and not much use has been made o...

Over-Tip-Rotor (OTR) liners have been investigated over the last decades as a technology to further reduce fan broadband noise in turbofan engines. It has been found that Over-Tip-Rotor liners suppress noise by conventional attenuation of acoustic waves and source modification effects. This paper describes a fundamental experiment to determine the...

Among the various noise sources related to duct fans, the noise generated by the tip leakage flow when interacts with the blade geometric singularities is one of the least understood noise sources. This paper deals with characterising the various tip noise generating mechanisms for a single-fixed aerofoil, as it is difficult to distinguish them in...

This paper investigates the noise generated by propeller-wing configuration at take-off condition with the propeller mounted upstream. This study makes use of various axisymmetric noise models developed for contra-rotating propellers to estimate the noise generated by propeller-wing configuration and later integrate them to estimate total noise. Fi...

Tip-leakage noise remains one of the least understood sources of noise in ducted rotors used in industry across different sectors including aerospace, automotive, and ventilation systems. Different technologies have been proposed to reduce tip leakage noise by treating either the duct casing over the tip rotor or the blade tip itself. This work des...

The aviation sector is rapidly evolving with more electric propulsion systems and a variety of new technologies of vertical take-off and landing manned and unmanned aerial vehicles. Community noise impact is one of the main barriers for the wider adoption of these new vehicles. Within the framework of a perception-driven engineering approach, this...

The present study investigates the efficacy of sinusoidal trailing-edge (TE) serrations as a passive means for the reductions of airfoil broadband noise, theoretically and experimentally. Comprehensive parametric studies were conducted to determine the effect of ser-ration amplitudes and wavelengths on the noise reduction performance of a National...

Experimental studies of a NACA 65(12)-10 airfoil with a sinusoidal leading-edge undulation (LEU) were carried out to simultaneously optimize its aerodynamic and aeroacoustic performances by considering the attached as well as the separated flow at the effective Reynolds number of 10^6, where the maximum lift was increased without sacrificing drag o...

Axialventilatoren werden in den meisten Fällen stromab von Schutzgittern, Wärmeübertrager oder Luftfilter eingesetzt. Durch die gestörte turbulente Zuströmung wird der induzierte Schalldruckpegel im Vergleich zur freien Anströmung erhöht. Vorderkantenmodifikationen, wie Zähnelungen, poröse Strukturen oder in Strömungsrichtung orientierte Schlitze s...

This paper deals with the effect of probe vibration on hot wire velocity measurements. In this paper we demonstrate that the mean flow has the effect of amplifying the effects of probe vibration such that even small levels of vibration can contaminate turbulence velocity measurements in high speed flows. A method for removing the effect of probe vi...

This paper presents an experimental study to investigate a novel, yet simple trailing edge treatment to enable aerofoil self-noise reduction with frequency-tuning capability based on the acoustical interference mechanism. Using a structurally-rigid slit trailing edge where the edges become parallel to the mean flow direction, it can facilitate a ph...

Overlapping propeller systems are currently used on some urban flight vehicles and will become increasingly common in future electric propulsion, since they provide one of the most compact platform volumes per unit thrust. This paper presents the results of a detailed experimental investigation of the dominant noise mechanisms due to two overlappin...

An experimental investigation on the acoustic and aerodynamic effect of permeable structures at airfoils and fan blades under distorted inflow conditions was performed. The study focuses on the position and the extent of the porous structure with respect to the leading edge. In a first step, aerodynamic and aeroacoustic measurements are carried out...

This paper presents a theoretical study of introducing a single gap or slot downstream of the leading edge of a thin rigid plate on aeroacoustic scattering. This is investigated as an elementary model for understanding the effect of downstream perforations on gust-aerofoil interaction noise. Across the slot it is supposed there is zero pressure jum...

This paper discusses the elements that make up a theoretical model for predicting the noise generated by a serrated trailing edge, and in particular, the required input to such a model; the wavenumber frequency spectra of the turbulence at the edge. It is proposed that this input, which is often modeled empirically, varies between a straight edge a...

This paper provides a preliminary theoretical investigation of the balance between rotor alone tonal and broadband noise. First, using well-published theory, the different source mechanisms for tonal and broadband noise are discussed and presented. Then, using these theoretical results, an extensive parametric study has been performed in which the...

Aerofoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge. Much work has been undertaken demonstrating the effectiveness by which serrations, or leading edge profiles, and porosity introduced onto the leading edge can substantially reduce broadband leading-edge interact...

A major source of the broadband noise in modern aeroengines is the interaction of fan wake turbulence with the downstream outlet guide vanes. The present paper investigates a three-dimensional numerical simulation of fan-OGV configuration in an annular duct using a frequency-domain Linearized Navier-Stokes solver coupled with a POD synthetic turbul...

We consider a finite perforated plate and study the effects of smoothly varying chordwise porosity on turbulence-aerofoil interaction noise. To study this problem, we use a novel Mathieu function collocation method, rather than a traditional Wiener-Hopf approach which would be unable to deal with chordwise varying quantities. Our main focus is on t...

Unmanned aerial vehicle (UAV) technologies are rapidly advancing due to the unlimited number of applications from parcel delivery to people transportation. As the UAV market expands, community noise impact will become a significant problem for public acceptance. Compact drone architectures based on contra-rotating propellers bring significant benef...

Overlapping propeller systems are currently used on some urban flight vehicles and will become increasingly common in future electric propulsion, since they provide one of the most compact platform volumes per thrust. This paper presents the results of a detailed experimental investigation of co-axial contra-rotating propeller configuration at hove...

This paper presents an optimisation approach for designing low-noise Outlet Guide Vanes (OGVs) for fan broadband noise generated due to the interaction of turbulence and a cascade of 2-dimensional aerofoils. The paper demonstrates the usage of Bayesian optimisation with constraints to reduce the computation cost of optimisation. The prediction is b...

This paper considers the effects of smoothly varying chordwise porosity of a finite perforated plate on turbulence-aerofoil interaction noise. The aeroacoustic model is made possible through the use of a novel Mathieu function collocation method, rather than a traditional Wiener–Hopf approach, which would be unable to deal with chordwise varying qu...

A benchmark dedicated to RANS-informed analytical methods for the prediction of turbofan rotor–stator interaction broadband noise was organised within the framework of the European project TurboNoiseBB. The second part of this benchmark focuses on the impact of the acoustic models. Twelve different approaches implemented in seven different acoustic...

A benchmark of Reynolds-Averaged Navier-Stokes (RANS)-informed analytical methods, which are attractive for predicting fan broadband noise, was conducted within the framework of the European project TurboNoiseBB. This paper discusses the first part of the benchmark, which investigates the influence of the RANS inputs. Its companion paper focuses on...

This paper is predominantly an experimental study into the reduction of turbulence - aerofoil interaction noise by the introduction of aerofoil porosity. In this paper we study three scenarios applied to at plates: (a) when the at plate is fully porous, (b) when the at plate is partially porous from the leading edge and (c) when porosity is introdu...

This paper addresses the usefulness of leading edge serrations for reducing aerofoil self-noise over a wide range of angles of attack. Different serration geometries are studied over a range of Reynolds number (Re =2e5-4e5). Design guidelines are proposed that permit noise reductions over most angles of attack. It is shown that serration geometries...

Aerofoil Turbulence Interaction (ATI) noise is an inviscid phenomenon generated by the impingement of turbulent flows onto the leading-edge of an aerofoil. This paper deals with a novel leading-edge serration geometry, composed of narrow slits, to reduce ATI noise. These profiles have been recently found to provide significantly better noise reduct...

Aerofoils operating in a turbulent floware an efficient source of noise radiation by scattering vorticity into sound at the leading edge. Much work has been undertaken demonstrating the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading edge interaction noise. However, mos...

The focus of this paper is on investigating the noise produced by an airfoil at high angles of attack over a range of Reynolds number Re≈2×10^5–4×10^5. The objective is not modeling this source of noise but rather understanding the mechanisms of generation for surface pressure fluctuations, due to a separated boundary layer, that are then scattered...

Leading-edge (LE) and trailing-edge (TE) noise due to the interaction of unsteady flow with the sharp edges of aerofoils are common in many engineering applications. One of the most widely used reduction methods is to use serrations, such as those of a sawtooth and a sinusoidal profile. The optimal serration geometry, however , remains largely unkn...

Axial fans have a major impact on the sound emission of technical systems. One of the common applications of low-pressure axial fans is their usage in air conditioning and cooling circuits. In most cases the fan operates downstream of a heat exchanger in this scheme. The suction side heat exchanger changes the upstream flow field of the fan, often...

Leading-edge serrations are studied extensively as a way of reducing leading-edge noise and have been shown to be able to reduce leading-edge noise significantly. Previous experiments showed that different serration geometries have different noise reduction capabilities. However, the optimal serration geometry has not been known. Consequently, ther...

This paper presents an analytic solution for gust-aerofoil interaction noise for flat plates with spanwise-varying periodic leading edges in uniform mean flow. The solution is obtained by solving the linear inviscid equations via separation of variables and the Wiener-Hopf technique, and is suitable for calculating the far-field noise generated by...

Aerofoils operating in a turbulent flow generate broadband noise by scattering vorticity into sound at the leading edge. Previous work has demonstrated the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading-edge noise. All of this work has focused on sinusoidal (single-wave...

Aerofoils operating in a turbulent flow generate broadband noise by scattering vorticity into sound at the leading edge. Previous work has demonstrated the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading edge noise. All of this work has focused on sinusoidal (single-wav...

The time-resolved velocity field (2D2C high-speed PIV) and surface pressure (pressure taps) of a stalled NACA0012 airfoil have been simultaneously measured. These measurements enable cross-evaluation of the velocity field and pressure time series. The present paper evaluates the flow field and surface pressure using POD, cross-correlation and condi...

This paper presents an analytic solution for the sound generated by an unsteady gust interacting with a semi-infinite at plate with a piecewise linear periodic leading edge. The Wiener-Hopf method is used in conjunction with a non-orthogonal coordinate transformation and separation of variables to allow analytical progress. A fully analytic solutio...

p>Aerofoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge. Much work has now been undertaken demonstrating the effectiveness by which serrations, or undulations, introduced onto the leading edge, can substantially reduce broadband leading edge interaction noise. Howev...

p>The turbulent wakes generated by a rotor interacting with outlet guide vanes is one of the dominant broadband noise sources in a turbofan engine. The present paper deals with the prediction of broadband noise due to the interaction of rotor wake turbulence with the OGV. The proposed approach aims to reproduce the two-point cross-spectral statisti...

This paper aims at evaluating the possibility of reducing the noise generated by the separated flow over an aerofoil, due to conditions near to or of stall, by the introduction of serrations on its leading edge. First of all the onset of the separation on the aerofoil surface and the associated noise have been investigated. Different serration geom...

Aerofoils operating in a turbulent flow are an efficient source of noise radiation by scattering vorticity into sound at the leading edge (LE). Much work has now been undertaken demonstrating the effectiveness of serrations, or undulations, introduced onto the LE can substantially reduce broadband LE interaction noise. However, all of this work is...

p>Reducing aircraft noise has become a significant political issue over the last decade, with the establish-ment of more demanding regulations concerning noise emissions. Aerofoil-Turbulence Interaction noise is an inviscid phenomenon generated by the impingement of turbulent flows on the leading-edge of an aerofoil. Occurring during the interactio...

This paper investigates the effects of local leading-edge geometry on unsteady aerofoil interaction noise. Analytical results are obtained by extending previous work for parabolic leading edges to leading edges of the form $x^{m}$ for $0 . Rapid distortion theory governs the interaction of an unsteady vortical perturbation with a rigid aerofoil in...

This paper presents an experimental investigation into the use of LE serrations for the reduction of trailing edge self-noise, at least for the NACA-65 aerofoil family. It is shown that the leading edge serrations are able to reduce the self-noise in a low frequency range at small and negative angles of attack. The exact mechanism of this reduction...

Fan broadband is one of the dominant noise sources on an aircraft engine, particularly at approach. The dominant noise generation mechanism is due to turbulent- aerofoil interaction noise (TAI). This thesis investigates the effect of changes in 2D aerofoil geometry on TAI noise. The main focus of this thesis is to attempt to reduce it through the d...

This paper presents the results of a detailed experimental investigation into the effectiveness of sinusoidal leading edge serrations on aerofoils for the reduction of the noise generated by the interaction with turbulent flow. A detailed parametric study is performed to investigate the sensitivity of the noise reductions to the serration amplitude...