Aeroacoustic analysis of slat tones

2021 ◽  
Vol 263 (1) ◽  
pp. 5650-5663
Author(s):  
Hasan Kamliya Jawahar ◽  
Syamir Alihan Showkat Ali ◽  
Mahdi Azarpeyvand
Keyword(s):  
Wavelet Transform ◽  
Surface Pressure ◽  
Wavelet Coefficient ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Stream Velocity ◽  
High Lift ◽  
Unsteady Surface Pressure ◽  
Slat Noise ◽  
Generation Mechanisms

Experimental measurements were carried out to assess the aeroacoustic characteristics of a 30P30N high-lift device, with particular attention to slat tonal noise. Three different types of slat modifications, namely slat cove filler, serrated slat cusp, and slat finlets have been experimentally examined. The results are presented for an angle of attack of α = 18 at a free-stream velocity of U = 30 m/s, which corresponds to a chord-based Reynolds number of Re = 7 x 10. The unsteady surface pressure near the slat region and far-field noise were made simultaneously to gain a deeper understanding of the slat noise generation mechanisms. The nature of the low-frequency broadband hump and the slat tones were investigated using higher-order statistical approaches for the baseline 30P30N and modified slat configurations. Continuous wavelet transform of the unsteady surface pressure fluctuations along with secondary wavelet transform of the broadband hump and tones were carried out to analyze the intermittent events induced by the tone generating resonant mechanisms. Stochastic analysis of the wavelet coefficient modulus of the surface pressure fluctuations was also carried out to demonstrate the inherent differences of different tonal frequencies. An understanding into the nature of the noise generated from the slat will help design the new generation of quite high-lift devices.

Method of Footprint Image Stitching Based on Multiscale SIFT Feature Matching

2013 ◽  
Vol 303-306 ◽  
pp. 1056-1059
Author(s):  
Sen Wang ◽  
Yin Hui Zhang ◽  
Zhong Hai Shi ◽  
Zi Fen He
Keyword(s):  
Wavelet Transform ◽  
Feature Matching ◽  
Wavelet Coefficient ◽  
Low Frequency ◽  
Original Method ◽  
Inverse Transformation ◽  
Image Stitching ◽  
Image Splicing ◽  
Sift Feature ◽  
Matching Pair

The image stitching method is widely used into the suspect's footprint information extraction. In order to improve the image detail and the matching precision, the Footprint map image stitching method which is based on the wavelet transform and the SIFT feature matching is put forward. The wavelet transform in this method is perform based on the pretreatment of image, move the low frequency wavelet coefficient to zero, adjusting thresholds of the high frequency wavelet coefficient and inverse transformation, then, use the SIFT to extract and match the key-points of the processed images. For the error matching pair of coarse match, you can use the RANSAC to filter them out. This article demonstrates its advantage through to the original image splicing comparisons. The experimental results show that the method display more clear detail and the precision of matching than the original method.

Experimental and Numerical Investigation of the Unsteady Surface Pressure in a Three-Stage Model of an Axial High Pressure Turbine

2004 ◽  
Vol 128 (2) ◽  
pp. 261-272 ◽  
Author(s):  
Carmen E. Kachel ◽  
John D. Denton
Keyword(s):  
High Pressure ◽  
Velocity Field ◽  
Surface Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Pressure Waves ◽  
Stage Model ◽  
Unsteady Pressure ◽  
Unsteady Surface Pressure ◽  
Blade Row

This paper presents the results of a numerical and experimental investigation of the unsteady pressure field in a three-stage model of a high pressure steam turbine. Unsteady surface pressure measurements were taken on a first and second stage stator blade, respectively. The measurements in the blade passage were supplemented by time resolved measurements between the blade rows. The explanation of the origin of the unsteady pressure fluctuations was supported by unsteady three-dimensional computational fluid dynamic calculations of which the most extensive calculation was performed over two stages. The mechanisms affecting the unsteady pressure field were: the potential field frozen to the upstream blade row, the pressure waves originating from changes in the potential pressure field, the convected unsteady velocity field, and the passage vortex of the upstream blade row. One-dimensional pressure waves and the unsteady variation of the pitchwise pressure gradient due to the changing velocity field were the dominant mechanisms influencing the magnitude of the surface pressure fluctuations. The magnitude of these effects had not been previously anticipated to be more important than other recognized effects.

Experimental and Unsteady Numerical Investigation of the Tip Clearance Noise of an Axial Fan

2013 ◽  
Author(s):  
Tao Zhu ◽  
Thomas H. Carolus
Keyword(s):  
Surface Pressure ◽  
Temporal Structure ◽  
Pressure Fluctuations ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Far Field ◽  
Axial Fan ◽  
Clearance Ratio ◽  
Wall Pressure Fluctuations ◽  
Unsteady Surface Pressure

The aerodynamic and aeroacoustic performance of axial fans are strongly affected by the unavoidable tip clearance. Two identical fan impellers but with different tip clearance ratio were investigated. Unsteady wall pressure fluctuations in the tip region of the rotating blades and on the interior wall of the duct type shroud and the overall sound radiated were analysed by an unsteady numerical Scale-Adaptive Simulation (SAS) and unsteady surface pressure measurements in both, the stationary and rotating system. Based on SAS-predicted pressure fluctuations on the blade surfaces the acoustic analogy according to Ffowcs Williams and Hawkings (FWH) was employed to calculate the sound pressure in the far field. In general, experimentally and numerically determined unsteady flow were found to be a tendentially good agreement. The spatial and temporal structure of the tip vortex system and the resulting unsteady pressure distribution on the surfaces in the vicinity of the blade tips was revealed in good detail. The vortices’ strength and trajectories as well as the unsteadiness are controlled by the size of the tip clearance and the operating point: As tip clearance is increased blade/vortex interaction becomes more prevalent and with it the unsteady surface pressure and eventually the sound radiated into the far field. The broadband tip clearance noise was acceptably predicted from the simulation results, while the prediction at discrete frequency should still be improved in the further work.

Variations in Upstream Vane Loading With Changes in Back Pressure in a Transonic Compressor

1998 ◽  
Vol 122 (3) ◽  
pp. 433-441 ◽  
Author(s):  
Douglas P. Probasco ◽  
Tim J. Leger ◽  
J. Mitch Wolff ◽  
William W. Copenhaver ◽  
Randall M. Chriss
Keyword(s):  
Surface Pressure ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Back Pressure ◽  
Bow Shock ◽  
Navier Stokes ◽  
Inlet Guide Vane ◽  
Transonic Compressor ◽  
Unsteady Surface Pressure ◽  
Upstream Pressure

Dynamic loading of an inlet guide vane (IGV) in a transonic compressor is characterized by unsteady IGV surface pressures. These pressure data were acquired for two spanwise locations at a 105 percent speed operating condition, which produces supersonic relative Mach numbers over the majority of the rotor blade span. The back pressure of the compressor was varied to determine the effects from such changes. Strong bow shock interaction was evident in both experimental and computational results. Variations in the back pressure have significant influence on the magnitude and phase of the upstream pressure fluctuations. The largest unsteady surface pressure magnitude, 40 kPa, was obtained for the near-stall mass flow condition at 75 percent span and 95 percent chord. Radial variation effects caused by the spanwise variation in relative Mach number were measured. Comparisons to a two-dimensional nonlinear unsteady blade/vane Navier–Stokes analysis show good agreement for the 50 percent span results in terms of IGV unsteady surface pressure. The results of the study indicate that significant nonlinear bow shock influences exist on the IGV trailing edge due to the downstream rotor shock system. [S0889-504X(00)00303-2]

Analysis and Simulation of Meteorological Wind Fields Based on Wavelet Transform

2014 ◽  
Vol 490-491 ◽  
pp. 1228-1236 ◽  
Author(s):  
Fo Rong Jin ◽  
Wei Rong Wang
Keyword(s):  
Wavelet Transform ◽  
Wavelet Coefficient ◽  
Low Frequency ◽  
Inertial Subrange ◽  
Target Velocity ◽  
Wind Fields ◽  
Transform Method ◽  
Time Frequency ◽  
Velocity Spectra ◽  
Energy Relations

In this work, we examined the non Gauss distribution characteristic and evolution law of the wavelet coefficient of a gust using wavelet transform; according to the time-frequency characteristic, the wavelet transform coefficients and the energy relations of the target velocity spectra are derived; the wavelet coefficient is generated using the cascade model reflecting the turbulent intermittent; the unsteady gust artificial generation method is established based on inverse wavelet transform; and the arbitrary unsteady fluctuation law can be generated by regulating the coefficient of low frequency. The results show that: the natural gust is in good agreement with Karman wind speed spectrum, meets the turbulence-5 / 3 law in the inertial subrange, and exhibits the nature of intermittence and local self-similarity; the artificial wind sequence based on the inverse wavelet transform method shows similar turbulence statistics with natural gust, with which, the effectiveness of the method is confirmed.

Unsteady Pressures on the Surface of a Ship Hull

2007 ◽  
Author(s):  
Michael Goody ◽  
Theodore Farabee ◽  
Yu-Tai Lee
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Pressure Measurement ◽  
Navier Stokes ◽  
Stream Velocity ◽  
Low Frequencies ◽  
Bow Wave ◽  
Lower Reynolds Number ◽  
Unsteady Surface Pressure ◽  
Layer Flow

The unsteady surface pressures caused by turbulent boundary layer flow are a source of sound and vibration. Unsteady surface pressure measurements at locations distributed on the surface of a ship model hull were carried out in order to characterize this source. The pressure measurement locations were distributed over the hull surface from 15% to 70% of the model length. There were several additional pressure measurement locations on the hull surface adjacent to the bow wave. The measurements were performed in the David Taylor Model Basin. The surface pressure spectra collapse to a single curve when scaled by canonical boundary layer variables at measurement locations aft of the bow wave. Additionally, measurements at several of these locations indicate that the pressure sources are convected at 50% to 80% of the free-stream velocity. Both of these observations are similar to equilibrium turbulent boundary layers. The measured surface pressure spectra compare well to predictions done using an empirical model that is based on historical, equilibrium, surface pressure spectra. At low frequencies, the measured surface pressure spectra also compare well to prediction done at lower Reynolds number using a Reynolds-Averged Navier-Stokes Statistical Model.

Variations in Upstream Vane Loading With Changes in Back Pressure in a Transonic Compressor

1998 ◽  
Author(s):  
Douglas P. Probasco ◽  
J. Mitch Wolff ◽  
William W. Copenhaver ◽  
Randall M. Chriss
Keyword(s):  
Surface Pressure ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Back Pressure ◽  
Bow Shock ◽  
Navier Stokes ◽  
Inlet Guide Vane ◽  
Transonic Compressor ◽  
Unsteady Surface Pressure ◽  
Non Linear

Dynamic loading of an inlet guide vane (IGV) in a transonic compressor is characterized by unsteady IGV surface pressures. This pressure data was acquired for two spanwise locations at a 105% speed operating condition, which produces supersonic relative Mach numbers over the majority of the rotor blade span. The back pressure of the compressor was varied to determine the effects from such changes. Strong bow shock interaction was evident in both experimental and computational results. Variations in the back pressure have significant influence on the magnitude and phase of the upstream pressure fluctuations. The largest unsteady surface pressure magnitude, 40 kPa, was obtained for the near stall mass flow condition at 75% span and 95% chord. Radial variation effects caused by the spanwise variation in relative Mach number were measured. Comparisons to a two-dimensional non-linear unsteady blade/vane Navier-Stokes analysis shows good agreement for the 50% span results in terms of IGV unsteady surface pressure. The results of the study indicate that significant non-linear bow shock influences exist on the IGV trailing edge due to the downstream rotor shock system.

Experimental and Numerical Investigation of the Unsteady Surface Pressure in a Three-Stage Model of an Axial High Pressure Turbine

2004 ◽  
Author(s):  
Carmen E. Kachel ◽  
John D. Denton
Keyword(s):  
High Pressure ◽  
Velocity Field ◽  
Surface Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Pressure Waves ◽  
Stage Model ◽  
Unsteady Pressure ◽  
Unsteady Surface Pressure ◽  
Blade Row

This paper presents the results of a numerical and experimental investigation of the unsteady pressure field in a three-stage model of a high pressure steam turbine. Unsteady surface pressure measurements were taken on a first and second stage stator blade respectively. The measurements in the blade passage were supplemented by time resolved measurements between the blade rows. The explanation of the origin of the unsteady pressure fluctuations was supported by unsteady three-dimensional computational fluid dynamic calculations of which the most extensive calculation was performed over two stage. The mechanisms affecting the unsteady pressure field were: the potential field frozen to the upstream blade row, the pressure waves originating from changes in the potential pressure field, the convected unsteady velocity field and the passage vortex of the upstream blade row. One-dimensional pressure waves and the unsteady variation of the pitchwise pressure gradient due to the changing velocity field were the dominant mechanisms influencing the magnitude of the surface pressure fluctuations. The magnitude of these effects had not been previously anticipated to be more important than other recognized effects.

scholarly journals Surface Pressure Fluctuations Produced by the Total Solar Eclipse of 1 August 2008

2013 ◽  
Vol 70 (3) ◽  
pp. 809-823 ◽  
Author(s):  
J. Marty ◽  
F. Dalaudier ◽  
D. Ponceau ◽  
E. Blanc ◽  
U. Munkhuu
Keyword(s):  
Gravity Waves ◽  
Surface Pressure ◽  
Solar Eclipse ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Ground Surface ◽  
Internal Gravity Waves ◽  
Total Solar Eclipse ◽  
Atmospheric Tides ◽  
Time Frequency

Abstract During a solar eclipse, the moon’s shadow progressively occults a part of Earth from the solar flux. This induces a cooling in the atmospheric layers that usually absorb the solar radiation. Since the eclipse shadow travels within the atmosphere at supersonic velocity, this cooling generates a planetary-scale bow wave of internal gravity waves. The purpose of this article is to estimate the surface atmospheric pressure fluctuations produced by the passage of the 1 August 2008 total solar eclipse and to compare these pressure fluctuations with those recorded by a temporary network of microbarographs and by the infrasound stations of the International Monitoring System. The surface pressure fluctuations expected at all the measurement sites are estimated using a linear spectral numerical model. It is shown that the cooling of both the ozonosphere and the troposphere can produce detectable pressure fluctuations at the ground surface but that the tropospheric cooling is likely to be the predominant source. Since the expected eclipse signals are in a frequency range that is highly perturbed by atmospheric tides and meteorological phenomena, the pressure fluctuations produced by these latter synoptic disturbances are characterized and removed from the recorded signals. Low-frequency gravity waves starting just after the passage of the eclipse are then brought to light at most measurement sites. The time–frequency characteristics of these waves are similar to those obtained from the model, which strongly suggests that these waves were produced by the passage of the 1 August 2008 solar eclipse.

Separated flow surface pressure fluctuations and pressure-velocity correlations on prolate spheroid

AIAA Journal ◽  
2000 ◽  
Vol 38 ◽  
pp. 266-274
Author(s):  
Michael C. Goody ◽  
Roger L. Simpson ◽  
Christopher J. Chesnakas
Keyword(s):  
Surface Pressure ◽  
Pressure Fluctuations ◽  
Separated Flow ◽  
Prolate Spheroid ◽  
Flow Surface
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