Effect on Sound Source Drift Caused by Angles Between Jet Flow Direction and Microphone Array or Sound Source Plane

2016 ◽  
Author(s):  
Zhe Shen ◽  
Yigang Wang ◽  
Zhigang Yang
Keyword(s):  
Wind Tunnel ◽  
Sound Source ◽  
Sound Propagation ◽  
Microphone Array ◽  
Flow Direction ◽  
Engineering Application ◽  
Jet Flow ◽  
Source Plane ◽  
Geometrical Acoustics ◽  
Beamforming Algorithm

When sound generated in jet flow propagates to outside of flow field, direction of sound propagation changes because of wave convection and refraction of shear layer. In wind tunnel, sound source drift appears when sound source is located with out-flow microphone array based on beamforming algorithm. In some cases, angles between jet flow direction and microphone array or sound source plane are inevitable due to geometric position, which increases the number of parameters affecting sound source drift distance. Geometrical acoustics and basic beamforming algorithm were used in this paper to deduce the relation between sound source drift and the angles. Equations for drift prediction and method for error reduction were given. Experimental verification was completed in a full-scale aero-acoustic wind tunnel with 2 loudspeakers set on an auto-body surface and microphone array with 120 channels. The experimental results prove that the equations for sound drift prediction in complicated geometric position relationship have a high accuracy, could help quick locating sound sources in engineering application.

Synthetic Sound Source Generation for Acoustical Measurements in Turbomachines

2013 ◽  
Author(s):  
Michael Bartelt ◽  
Juan D. Laguna ◽  
Joerg R. Seume
Keyword(s):  
Wind Tunnel ◽  
Sound Source ◽  
Sound Propagation ◽  
Microphone Array ◽  
Sound Field ◽  
Acoustic Mode ◽  
Acoustic Excitation ◽  
Noise Emission ◽  
Noise Sources ◽  
Sound Fields

One of the greatest challenges in modern aircraft propulsion design is the reduction of the engine noise emission in order to develop quieter aircrafts. In the course of a current research project, the sound transport in low pressure turbines is investigated. For the corresponding experimental measurements, a specific acoustic excitation system is developed which can be implemented into the inlet of a turbine test rig and into an aeroacoustic wind tunnel. This allows for an acoustic mode generation and a synthesis of various sound source patterns to simulate typical turbomachinery noise sources such as rotor-stator interaction, etc. The paper presents the acoustical and technical design methodology in detail and addresses the experimental options of the system. Particular attention is paid to the design and the numerical optimization of the acoustic excitation units. To validate the sound generator during operation, measurements are performed in an aeroacoustic wind tunnel. For this purpose, an in-duct microphone array with a specific beamforming algorithm for hard-walled ducts is developed and applied to identify the source locations. The synthetically excited sound fields and the propagating acoustic modes are measured and analyzed by means of modal decomposition techniques. The measurement principles and the results are discussed in detail and it is shown that the intended sound source is produced and the intended sound field is excited. This paper shall contribute to help guide the development of excitation systems for aeroacoustic experiments to better understanding the physics of sound propagation within turbomachines.

An Improved Correction Method for Sound Source Drift in A Jet Flow and Its Application to A Wind Tunnel Measurement

2015 ◽  
Vol 101 (3) ◽  
pp. 642-649 ◽  
Author(s):  
Yigang Wang ◽  
Jiashun Yang ◽  
Qing Jia ◽  
Zhigang Yang ◽  
Zhe Shen
Keyword(s):  
Wind Tunnel ◽  
Sound Source ◽  
Jet Flow ◽  
Correction Method ◽  
Wind Tunnel Measurement

The Effects of the Jet-Flow on Sound Propagation in Low-Speed Wind Tunnel

2012 ◽  
Vol 226-228 ◽  
pp. 368-373
Author(s):  
Yi Gang Wang ◽  
Jia Shun Yang ◽  
Yang Yang ◽  
Zhi Gang Yang
Keyword(s):  
Wind Tunnel ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Sound Propagation ◽  
Prediction Method ◽  
Test Sample ◽  
Jet Flow ◽  
Pressure Level ◽  
High Frequency Signal ◽  
Low Speed Wind Tunnel

Based on the open-jet aero-acoustic wind tunnel, an experimental study was made to research the effects of the jet-flow on sound propagation. This study is focused on the changes of the direction of the sound propagation, the changes of the sound pressure level, the phenomenon of tone broadening and the availability of the existing prediction method for sound propagation in jet-flow. The results indicate that the influence of the jet-flow on the value of the noise source shift varies along the direction of the jet-flow and there is no regular influence on the sound pressure level. In addition, the flow around the test sample has affected the sound propagation, and the phenomenon of tone broadening exists when high frequency signal is used. The study also reveals the limitation of the application of the existing prediction method, because the model it used is too simple.

Effect of Blade Tip Geometry on Tip Flow and Heat Transfer for a Blade in a Low Speed Cascade

2003 ◽  
Author(s):  
Vikrant Saxena ◽  
Hasan Nasir ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Wind Tunnel ◽  
Flow Direction ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Transfer Coefficients ◽  
Wake Effect ◽  
Low Speed ◽  
Heat Transfer Coefficients ◽  
Blade Tip

A comprehensive investigation of the effect of various tip sealing geometries is presented on the blade tip leakage flow and associated heat transfer of a scaled up HPT turbine blade in a low-speed wind tunnel facility. The linear cascade is made of four blades with the two corner blades acting as guides. The tip section of a HPT first stage rotor blade is used to fabricate the 2-D blade. The wind tunnel accommodates an 116° turn for the blade cascade. The mainstream Reynolds number based on the axial chord length at cascade exit is 4.83 × 105. The upstream wake effect is simulated with a spoked wheel wake generator placed upstream of the cascade. A turbulence grid placed even farther upstream generates the required free-stream turbulence of 4.8%. The center blade has a tip clearance gap of 1.5625% with respect to the blade span. Static pressure measurements are obtained on the blade surface and the shroud. The effect of crosswise trip strips to reduce leakage flow and associated heat transfer is investigated with strips placed along the leakage flow direction, against the leakage flow and along the chord. Cylindrical pin fins and pitch variation of strips over the tip surface are also investigated. Detailed heat transfer measurements are obtained using a steady state HSI-based liquid crystal technique. The effect of periodic unsteady wake effect is also investigated by varying the wake Strouhal number from 0. to 0.2, and to 0.4. Results show that the trip strips placed against the leakage flow produce the lowest heat transfer on the tips compared to all the other cases with a reduction between 10–15% compared to the plain tip. Results also show that the pitch of the strips has a small effect on the overall reduction. Cylindrical pins fins and strips along the leakage flow direction do not decrease the heat transfer coefficients and in some cases enhance the heat transfer coefficients by as much as 20%.

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