scholarly journals Time domain broadband noise predictions for non-cavitating marine propellers with wall pressure spectrum models

2021 ◽  
Vol 13 ◽  
pp. 75-85
Author(s):  
Woen-Sug Choi ◽  
Suk-Yoon Hong ◽  
Jee-Hun Song ◽  
Hyun-Wung Kwon ◽  
Il-Ryong Park ◽  
...  
Keyword(s):  
Time Domain ◽  
Broadband Noise ◽  
Wall Pressure ◽  
Marine Propellers

Prediction of Broadband Noise for Non-cavitation Hydrofoils using Wall-Pressure Spectrum Models

2019 ◽  
Vol 25 (6) ◽  
pp. 765-771
Author(s):  
Woen-Sug Choi ◽  
◽  
Seung-Jin Jeong ◽  
Suk-Yoon Hong ◽  
Jee-Hun Song ◽  
...  
Keyword(s):  
Broadband Noise ◽  
Wall Pressure

scholarly journals A New Time Domain Formulation for Broadband Noise Predictions

2002 ◽  
Vol 1 (3) ◽  
pp. 207-240 ◽  
Author(s):  
J. Casper ◽  
F. Farassat
Keyword(s):  
Surface Pressure ◽  
Time Domain ◽  
Isotropic Turbulence ◽  
Time Derivative ◽  
Broadband Noise ◽  
Alternative Form ◽  
Test Case ◽  
Surface Integral ◽  
Constant Frequency ◽  
Unsteady Surface Pressure

A new analytic result in acoustics called “Formulation 1B,” proposed by Farassat, is used to compute the loading noise from an unsteady surface pressure distribution on a thin airfoil in the time domain. This formulation is a new solution of the Ffowcs Williams-Hawkings equation with the loading source term. The formulation contains a far field surface integral that depends on the time derivative and the surface gradient of the pressure on the airfoil, as well as a contour integral on the boundary of the airfoil surface. As a first test case, the new formulation is used to compute the noise radiated from a flat plate, moving through a sinusoidal gust of constant frequency. The unsteady surface pressure for this test case is analytically specied from a result based on linear airfoil theory. This test case is used to examine the velocity scaling properties of Formulation 1B and to demonstrate its equivalence to Formulation 1A of Farassat. The new acoustic formulation, again with an analytic surface pressure, is then used to predict broadband noise radiated from an airfoil immersed in homogeneous, isotropic turbulence. The results are compared with experimental data previously reported by Paterson and Amiet. Good agreement between predictions and measurements is obtained. Finally, an alternative form of Formulation 1B is described for statistical analysis of broadband noise.

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

2013 ◽  
Author(s):  
Tao Zhu ◽  
Thomas H. Carolus
Keyword(s):  
Pressure Fluctuations ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Broadband Noise ◽  
Wall Pressure ◽  
Tip Clearance ◽  
Dipole Source ◽  
Vortex System ◽  
Rans Simulation ◽  
Wall Pressure Fluctuations

The aerodynamic and aeroacoustic performance of axial fans are strongly affected by the unavoidable tip clearance. Three identical fan impellers but with different tip clearance ratio were investigated. Details of the time averaged tip flow were analysed by a numerical RANS-simulation. 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 measured. As the tip clearance is increased, overall fan pressure rise and efficiency drop, the onset of the rotating stall moves to higher flow rates and broadband noise is found to become dominant in the spectrum. The RANS simulation revealed a vortex system consisting of three different vortices in the tip region. Their strength and trajectories are controlled by the size of the tip clearance and the fan’s operating point. Measurements showed that these vortices impose tonal and — more pronounced — broadband pressure fluctuations on stationary and rotating walls in the vicinity of the blade tip. The tip vortex system is the main driver of the unsteady flow in the tip region. As tip clearance is increased the unsteady wall pressure becomes more developed and with it the sound radiated by the fan. Hence it is concluded that these vortex induced pressure fluctuations form the dipole source mechanism of the noise observed. This hypothesis is supported by a preliminary correlation analysis.

Prediction of Rotorcraft Broadband Trailing-Edge Noise and Parameter Sensitivity Study

2020 ◽  
Vol 65 (4) ◽  
pp. 1-14
Author(s):  
Sicheng (Kevin) Li ◽  
Seongkyu Lee
Keyword(s):  
Pitch Angle ◽  
Twist Angle ◽  
Prediction Method ◽  
Sensitivity Study ◽  
Broadband Noise ◽  
Wall Pressure ◽  
Operating Parameters ◽  
Trailing Edge ◽  
Viscous Boundary Layer ◽  
Trailing Edge Noise

This paper investigates the effects of rotorcraft design and operating parameters on trailing-edge noise. A rotor trailing-edge noise prediction method is first developed where the aerodynamics and the turbulence wall pressure spectrum near the trailing edge on airfoils are predicted by a combination of the standard blade element momentum theory , a viscous boundary-layer panel method, and a recently developed empirical wall pressure spectrum model. The coordinate transformations are combined with the Amiet model to predict far-field noise. Compared to experimental data, the validation of this method demonstrates its advantages and validity for airfoil and rotorcraft broadband noise predictions. Then, this method is used to study the effects of rotorcraft design and operating parameters on rotor trailing-edge noise. It is found that helicopter broadband noise scales with the 4.5th to 5.0th power of the tip Mach number in which the range is determined by the typical helicopter collective pitch angle in operation. Detailed trend analyses of noise levels as a function of frequency are presented in terms of the collective pitch angle, twist angle, rotor solidity, rotor radius, disk loading, and number of blades. It is found that the collective pitch angle, twist angle, and chord length make noticeable impacts on low- and midfrequency noise. Finally, a semianalytic model is presented to predict the directivity and geometric attenuation of rotor trailing-edge noise.

Acoustic-Reflex Dynamics for Pulsed Signals

1978 ◽  
Vol 21 (2) ◽  
pp. 295-308
Author(s):  
Terry L. Wiley ◽  
Raymond S. Karlovich
Keyword(s):  
Duty Cycle ◽  
Acoustic Impedance ◽  
Normal Hearing ◽  
Broadband Noise ◽  
Threshold Shift ◽  
Temporary Threshold Shift ◽  
Acoustic Reflex ◽  
Stapedius Muscle ◽  
Duty Cycles

Contralateral acoustic-reflex measurements were taken for 10 normal-hearing subjects using a pulsed broadband noise as the reflex-activating signal. Acoustic impedance was measured at selected times during the on (response maximum) and off (response minimum) portions of the pulsed activator over a 2-min interval as a function of activator period and duty cycle. Major findings were that response maxima increased as a function of time for longer duty cycles and that response minima increased as a function of time for all duty cycles. It is hypothesized that these findings are attributable to the recovery characteristics of the stapedius muscle. An explanation of portions of the results from previous temporary threshold shift experiments on the basis of acoustic-reflex dynamics is proposed.

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