Propeller Noise Research Articles

Low-frequency interior noise in prop-driven aircrafts: Sources and control methodologies

Nowadays, noise has turned into one of the most important among the environmental factors on which industry sets down a big part of its efforts and concerns. The recognition of noise as a serious health hazard is a development of modern times. Too much noise obviously impairs our physical and mental existence and therefore it is reasonable to pursue Technology Assessment concerning noisy technologies. The conflicts of interest associated with noise that arise from the operation of airports are well known. Propeller noise is most dominant at low frequencies (below 500 Hz) where traditional passive treatments have only little effect. The many factors contributing to the sound field inside propeller aircraft have led to extensive research directed toward identifying and improving techniques for interior noise reduction.

Passive tracking of autonomous underwater vehicles (AUVs) using a low-cost acoustic data collection system

One challenge to harbor security is monitoring and tracking autonomous underwater vehicle (AUV) activity. A self-contained low-cost acoustic data collection system (acbox) has been developed and demonstrated for this purpose. The acbox consists of an 8-element configurable off-the-shelf hydrophone array, a data acquisition system, a GPS for timing and navigation, and a computer for data logging and processing. Noise data on the Bluefin SandShark and Bluefin 21-inch AUVs were collected using the configurable array in the Charles River and Massachusetts Bay. From this experiment, AUV noise characteristics were determined. The bearing to the AUV was estimated based on beamformed and frequency filtered data, and compared to logged AUV position. The bearing estimates based on propeller noise were consistent with the reported AUV position. These results for range estimation and filtering bearing were tested to provide improved vehicle localization. Performance in the presence of boat noise was also assessed. Moving forward, this work will be expanded to tracking AUVs from other AUVs for collision-avoidence and behavioral analysis for security monitoring applications. [Work supported by Battelle, DARPA, and Draper.]

A study on the influence of hull wake on model scale cavitation and noise tests for a fast twin screw vessel with inclined shaft

The study of ship underwater radiated noise is nowadays a topic of great and largely recognized importance. This is due to the fact that in the last decades, the problem of the impact of anthropogenic noise on marine life has been addressed with higher emphasis, giving rise to different efforts aimed to the analysis of its effects on different organisms and, in parallel, to means for the reduction of shipping noise. In this context, attention is focused on the propeller noise, which, in cavitating conditions, may represent the most important noise source of the ship. The propeller noise has been studied for long time with different approaches. One of the most effective approaches is represented by model scale testing in cavitation tunnels or similar facilities. Despite having been adopted for several years, radiated noise experiments in model scale are usually affected by significant scale effects and technical issues. One of these aspects is represented by the correct modelling of the propeller inflow; different techniques are adopted, depending on the facility, in order to reproduce a certain target wake. One of the main problems is to define this target wake, which should in principle coincide with the ship wake; as it is well known, it is usually derived from model scale towing tank measurements, with the necessity for the prediction of the full-scale wake field. Starting from the outcomes of a previous work on the influence of different approaches for the prediction of the full-scale wake field for a single screw ship, in this work, attention is focused on the case of a fast twin screw vessel, analysing the different issues which may be connected to this hull form.

멀티로터형 무인항공기 프로펠러의 고효율 및 저소음 설계를 위한 공력 소음 예측 기법 개발

멀티로터형 무인항공기는 군사용 목적뿐 아니라 항공 촬영 및 무인 택배 수단 등 민간 산업까지 그 활용 범위를 넓혀가고 있다. 무인항공기의 보다 폭넓은 활용을 위해서는 추진체인 프로펠러의 공력 효율 개선과 소음의 저감을 위한 연구가 선행되어야 하며, 이는 주어진 환경에서 공력 성능 및 소음을 예측할 수 있는 기술이 바탕이 되어야만 가능하다. 본 연구에서는 소형 무인항공기 프로펠러를 대상으로 공력 및 소음 예측 기법을 개발하고, 실제 측정을 통한 결과와의 비교를 통해 검증하였다. 분당 회전수의 변화에 따른 추력 및 토크와 주어진 위치에서의 주파수 스펙트럼 예측에서 모두 예측 기법의 신뢰성을 확보하였으며, 이를 통해 프로펠러의 형상 설계에 기반이 될 수 있는 기틀을 마련하였다. Multi-rotor type UAV (Unmanned Aerial Vehicle)s are expanding their applications not only for military purposes but also for private industries such as aerial photography and unmanned delivery vehicles. For wider use of unmanned aerial vehicles, studies should be carried out to improve aerodynamic efficiency and reduce noise of propellers, which can be achieved based on techniques of predicting aerodynamic performance and noise in a given environment. In this study, aerodynamic and noise prediction techniques were developed for a small unmanned aerial vehicle propeller, and it was verified by comparing it with actual measurement results. Thrust and torque due to the change of r/min and the frequency spectral prediction at a given position secured the reliability of the prediction method, which provides a basis for the shape design of the propeller.

An Experimental Study on the Effect of IS700 Coating on the Cavitation Inception and Development, and Noise Reduction of a Marine Propeller

In this paper, cavitation inception and development conditions are studied for five-blade propellers by experiments carried out in cavitation tunnel. Propeller noise is measured in different operating conditions for uncoated and coated propellers and also, the effects of silicone foul release (FR) coating, inter sleek 700 (IS700), are investigated on the cavitation delay and noise reduction of a marine propeller in cavitation tunnel. Finally, results are presented in low advance coefficients for cavitation inception and development, and noise reduction. These results can be applied as a reference for validating this propeller model in numerical simulations.

Evaluation of the influence of the number of blades and diameter on propeller noise

The article presents the results of computational and experimental research of the effect of the number of blades and the diameter on the noise of the propeller operating at Reynolds numbers of more than 106. It is shown that an increase in the number of blades while maintaining the aerodynamic and geometric similarity of the propellers and constant Mach number of the circumferential velocity leads to significant reduction of aerodynamic load noise. At the same time the displacement noise and the broadband noise increase insignificantly. Expressions are proposed that can be used to assess the effect of the diameter and the number of blades on the tonal noise and the noise of the trailing edge of the propeller provided the propeller thrust is constant. Measurements of the acoustic characteristics of light aircraft Yak-18T with two- and three-bladed propellers, MAI-223M and the F30, performed at the local aerodrome in static conditions qualitatively confirmed the estimates of the effect of the diameter and number of blades on the propeller noise. Increasing the number of blades leads to a noticeable decrease in the acoustic efficiency of engine-propeller power plants.

Evaluation of the cavitation inception speed of the ship propeller using acceleration on its adjacent structure

Cavitation noise is strongly restricted by the Navy because this noise can be detected by the sonar systems installed on enemy ships to locate a ship. When cavitation is started, the high-frequency broadband noise increases modulated with shaft rotation and propeller blade passing frequencies. Therefore, the Cavitation inception speed (CIS) is typically detected using the Detection of envelope modulation on noise (DEMON) analysis to identify the underwater propeller noise. Since the CIS varies based on the ship’s condition and sea state, realtime CIS monitoring is required. In this paper, a CIS detection method that evaluates the acceleration on the hull adjacent to the propeller was proposed and verified through experimentation.

Underwater radiated noise prediction for a submarine propeller in different flow conditions

International Maritime Organisation (IMO) and other bodies have been trying to set-up guidelines and regulations to reduce/limit noise levels at sea which influence marine life in particular marine mammals and certain fish types. Ships with low noise characteristics will be a must in the near future for almost all ship types. However for special ships, such as naval surface vessels, fishing vessels, submarines, etc. this has already been an issue because of their operational requirements. The propeller is one of the main sources of underwater noise generated by ships. Therefore, it is important to predict and control the underwater noise characteristics of propellers. In this respect, the main objective of this study is to calculate propeller radiated noise numerically. Propeller noise has been investigated numerically for the INSEAN E1619 submarine propeller in open water, behind a generic DARPA suboff submarine and within imposed wake cases at non-cavitating conditions due to their deeply submerged operations. Flow around the propeller is solved with a commercial CFD software using Unsteady Reynolds Averaged Navier–Stokes (URANS), while hydro-acoustic analysis is performed using a model based on Ffowcs-Williams and Hawkings equation. This paper reports the results of the study. The paper also includes the details of the bodies and discusses further improvement of the methodology applied.

Using Taguchi method for designing wedge-shaped structures for an acoustically non-reflecting test section

In the present article, optimal design of a wedge-shaped structure that is added to an acoustically non-reflecting test section in a cavitation tunnel is examined. This is done to decrease the propeller noise propagation. The proposed structure resembles a check valve which causes the propagated sound to be trapped in a space between the wedge-shaped structure and the wall. Sound loses its energy due to receiving a multitude of impacts. The acoustic analyses are performed for the source located in the center and three other asymmetrical sources. Initially, five parameters are analyzed on three levels and 27 tests are designed applying Taguchi’s method. After 27 tests, optimal values of the designated parameters are found for the sound source located at the center. To obtain more accurate values, the parameters are defined at five levels around the optimally obtained values and 25 tests are designed for each source. Finally, following 100 tests, the accurate optimal values of the considered parameters are obtained. Analyzing the final structure, the calculated results compared with 100 tests, displays the highest performance.

Determining the Hydro-acoustic Characteristics of the Ship Propeller in Uniform and Non-uniform Flow

This research has been carried out to determine the marine propeller hydro-acoustic characteristics by Reynolds-Averaged Navier-Stokes (RANS) solver in both uniform and non-uniform wake flow at different operating conditions Wake flow can cause changes in pressure fluctuation and gas effect on propeller noise spectrum. Noise is generated by the induced trailing vortex wake and induced pressure pulses. The two-step Fflowcs Williams and Hawkings (FW-H) equations are used to calculate hydrodynamic pressure and its performance as well as sound pressure level (SPL) at various points around the propeller. The directivity patterns of this propeller and accurate explanation of component propeller noise are discussed. Comparison of the numerical results shows good agreement with the experimental data. Based on these results, effects of wake flow and operating conditions on the noise reduction are investigated.

Noise Localization Method for Model Tests in a Large Cavitation Tunnel Using a Hydrophone Array

Model tests are performed in order to predict the noise level of a full ship and to control its noise signature. Localizing noise sources in the model test is therefore an important research subject along with measuring noise levels. In this paper, a noise localization method using a hydrophone array in a large cavitation tunnel is presented. The 45-channel hydrophone array was designed using a global optimization technique for noise measurement. A set of noise experiments was performed in the KRISO (Korea Research Institute of Ships & Ocean Engineering) large cavitation tunnel using scaled models, including a ship with a single propeller, a ship with twin propellers and an underwater vehicle. The incoherent broadband processors defined based on the Bartlett and the minimum variance (MV) processors were applied to the measured data. The results of data analysis and localization are presented in the paper. Finally, it is shown that the mechanical noise, as well as the propeller noise can be successfully localized using the proposed localization method.

Numerical and experimental propeller noise investigations

The standard propeller has been investigated in model scale, using medium size cavitation tunnel. The hydroacoustic characteristics of propellers under different loading conditions have been investigated. Additionally the presented experimental results have been used for the verification of applied numerical approach. During both numerical and experimental analyses non-uniform inflow propeller’s conditions have been adapted. Good correlations of both kinds of results have been noticed and highlighted.

Scattering effect of submarine hull on propeller non-cavitation noise

This paper investigates the non-cavitation noise caused by propeller running in the wake of submarine with the consideration of scattering effect caused by submarine׳s hull. The computation fluid dynamics (CFD) and acoustic analogy method are adopted to predict fluctuating pressure of propeller׳s blade and its underwater noise radiation in time domain, respectively. An effective iteration method which is derived in the time domain from the Helmholtz integral equation is used to solve multi-frequency waves scattering due to obstacles. Moreover, to minimize time interpolation caused numerical errors, the pressure and its derivative at the sound emission time is obtained by summation of Fourier series. It is noted that the time averaging algorithm is used to achieve a convergent result if the solution oscillated in the iteration process. Meanwhile, the developed iteration method is verified and applied to predict propeller noise scattered from submarine’s hull. In accordance with analysis results, it is summarized that (1) the scattering effect of hull on pressure distribution pattern especially at the frequency higher than blade passing frequency (BPF) is proved according to the contour maps of sound pressure distribution of submarine׳s hull and typical detecting planes. (2) The scattering effect of the hull on the total pressure is observable in noise frequency spectrum of field points, where the maximum increment is up to 3dB at BPF, 12.5dB at 2BPF and 20.2dB at 3BPF. (3) The pressure scattered from hull is negligible in near-field of propeller, since the scattering effect surrounding analyzed location of propeller on submarine’s stern is significantly different from the surface ship. This work shows the importance of submarine׳s scattering effect in evaluating the propeller non-cavitation noise.

Vibration Environment and the Rockets

Rockets are subjected to vibrations in various operational phases. Source of vibration may be due to air turbulence, propeller noise, engine noise, stage separation, pyro ignition, release mechanism etc. Some of the sections of rocket houses electronic equipments for data acquisition, navigation purposes etc. Any Structure possessing mass and elasticity vibrate under external disturbances. Electronic equipment can be subjected to many different forms of vibration over a wide range of frequencies and acceleration levels. Vibration is usually considered to be an detrimental condition and can produce many different types of failures in electronic equipment. It is always an endeavour to alleviate or minimize the vibration amplitudes. Wide variety of structures and their components are susceptible to vibration as they are subjected to time dependent forces. If the vibration amplitude of structure escalates to the upper levels, the failure of structures takes place. Vibration suppression has greater significance for aero-space structures, which houses sophisticated electronic equipments, as the high vibration amplitudes hinder the performance of such equipments. In this study it is demonstrated that Tuned Mass Dampers (TMDs) placed with individual modal tuning shows satisfactory performance for the structure subjected to wide band harmonic excitation, transient or random excitations.

Measurement of noise and its correlation to performance and geometry of small aircraft propellers

A set of small model and UAV propellers is measured both in terms of aerodynamic performance and acoustic noise under static conditions. Apart from obvious correlation of noise to tip speed and propeller diameter the influence of blade pitch, blade pitch distribution, efficiency and shape of the blade is sought. Using the measured performance data a computational model for calculation of aerodynamic noise of propellers will be validated. The range of selected propellers include both propellers designed for nearly static conditions and propellers that are running at highly offdesign conditions, which allows to investigate i.e. the effect of blade stall on both noise level and performance results.

Cyclostationarity Based Sonar Signal Processing

This paper presents a reliable method for target vessel identification in passive sonar by exploiting the underlying periodicity of propeller noise signal, using the principles of cyclostationarity. In conventional signal processing methods, random signals are treated as statistically stationary and the parameters of the underlying physical mechanism that generates the signal would not vary in time. However, for most manmade signals, some parameters vary periodically with time and this requires that random signals be modeled as cyclostationary. In the field of sonar, the propeller noise signal generated by underwater vessels is cyclostationary. As a ship propagates in the sea, noise generated during the collapse of cavitation-induced bubbles are modulated by the rotating propeller shaft and this results in characteristic amplitude modulated random noise signal, which can be detected using passive sonar. Processing these signals, the number of blades and the shaft frequency of the propeller can be identified. In this work, cyclostationary processing technique is introduced for processing propeller noise signal and it is observed to provide better noise immunity. A detailed comparison with the conventional DEMON processing is also presented.

Feasibility study into a computational approach for marine propeller noise and cavitation modelling

There is increased interest in the ability to predict the noise associated with commercial ship propellers. Key components of the computational analysis process are considered for two test cases and the future direction in resolving the associated challenges is presented. Firstly, the Potsdam Propeller Test Case is used to compute tonal blade passage noise using the Ffowcs Williams–Hawkings acoustic analogy. Cavitation extents predicted using the Sauer and Schnerr mass transfer model agree well with the experiment but show little unsteadiness due to URANS being used. A complementary study of initial results from the study of cavitation noise modelling attempt is presented for a NACA0009 section, used as a simplified representation of a propeller blade. Large Eddy Simulation and FW-H acoustic analogy are used in order to estimate the cavitation-induced noise. Results indicate that the discussed approach provides the means for identifying low-frequency noise generation mechanisms in the flow, but does not allow for the fine-scale bubble dynamics or shockwave formation to be resolved. It is concluded that the discussed approach is a viable option to predict large parts of the marine propeller noise spectra but still further work is needed in order to account for the broadband components.

Analysis of noise behaviour for marine propellers under cavitating and non-cavitating conditions

In this study, the hydrodynamics and noise behaviour of marine propellers are examined through finite volume method under various operational conditions. The hydrodynamics of these propellers are studied both numerically and experimentally, and the characteristic curves are produced. Sheet cavitation inception and development conditions are also considered in order to understand the impact of different rotational speeds on propeller noise. Ffowcs Williams and Hawkings equations are used to extract the total sound pressure levels under non-cavitating and sheet cavitating conditions. Finally, the impact of cavitation on increasing the propeller noise is thoroughly explored and the results are presented.

English

The volume of general aviation transport is increasing and consequently this gives rise to the need for reducing noise levels while improving or at least maintaining the same level of aerodynamic performance. This can be achieved through the use of modern propellers and engines. In this paper we present a methodology to study and predict the installed propeller noise at the same time with the aerodynamic characterization, through the use of unsteady CFD and Acoustic-Analogies analysis. The analysis shows the influence of different acoustic sources generated by the installed propeller on the far field noise by monitoring the monopoles and dipoles with and without taking into account the quadrupoles. In this way we can observe the influence of the distance from the propeller to the engine intake on the overall sound. Time averaged aerodynamic performances are presented along with instantaneous results.

Turboprop aircraft noise: Advancements and comparison with flyover data

AbstractThis paper contributes to the prediction of aircraft noise. The framework of our study is based on a comprehensive analysis, which includes sub-models for airframe, propulsion and propeller noise. The sources models are complemented by various accounts of interference phenomena, including fuselage scattering, propeller shielding, wing and flap effects. The propagation of the acoustic pressures from the noise sources is done through a number of additional sub-models, which include spherical spreading, Doppler effects, ground reflection, shear winds and temperature gradients through the atmosphere. We present some fly-over noise data. The data include measurements by 13 microphones at community locations, meteorological data, and flight recorder data packs, which provide the complete state of the aircraft along the noise trajectory. Examples of verification are shown for the turboprop airplane Dash8-Q400, both on approach and departure. A sensitivity analysis is carried out to investigate the importance of the uncertainty effects, which are split between internal (aircraft and propulsion), external (atmospheric environment), and aircraft position.