scholarly journals Aeroacoustic noise reduction by application of end plates on wall-mounted finite airfoils

2021 ◽  
Vol 62 (5) ◽  
Author(s):  
Erik Schneehagen ◽  
Thomas F. Geyer ◽  
Ennes Sarradj ◽  
Danielle J. Moreau
Keyword(s):  
Noise Reduction ◽  
Microphone Array ◽  
Boundary Layer Transition ◽  
Tip Vortex ◽  
Layer Transition ◽  
Aeroacoustic Noise ◽  
End Plate ◽  
Array Measurements ◽  
Field Noise ◽  
Naca 0012

Abstract One known method to reduce vortex shedding from the tip of a blade is the use of end plates or winglets. Although the aerodynamic impact of such end plates has been investigated in the past, no studies exist on the effect of such end plates on the far-field noise. The aeroacoustic noise reduction of three different end-plate geometries is experimentally investigated. The end plates are applied to the free end of a wall-mounted symmetric NACA 0012 airfoil and a cambered NACA 4412 airfoil with an aspect ratio of 2 and natural boundary layer transition. Microphone array measurements are taken in the aeroacoustic open-jet wind tunnel at BTU Cottbus-Senftenberg for chord-based Reynolds numbers between 75,000 and 225,000 and angles of attack from 0$$^\circ$$ ∘ to 30$$^\circ$$ ∘ . The obtained acoustic spectra show a broad frequency hump for the airfoil base configurations at higher angles of attack that is attributed to tip noise. Hot-wire measurements taken for one configuration show that the application of an end plate diffuses the vorticity at the tip. The aeroacoustic noise contribution of the tip can be reduced when the endplates are applied. This reduction is most effective for higher angles of attack, when the tip vortex is the dominant sound source. Graphic abstract

Large Eddy Simulation of Periodic Wake Impact on Boundary Layer Transition Mechanisms on a Highly Loaded Low-Pressure Turbine Blade

2020 ◽  
Author(s):  
Benjamin Winhart ◽  
Martin Sinkwitz ◽  
Andreas Schramm ◽  
Pascal Post ◽  
Francesca di Mare
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Array Measurements ◽  
Numerical Predictions ◽  
Large Eddy ◽  
Highly Loaded

Abstract In the proposed paper the transient interaction between periodic incoming wakes and the laminar separation bubble located on the rear suction surface of a typical, highly loaded LPT blade is investigated by means of highly resolved large-eddy simulations. An annular, large scale, 1.5-stage LPT test-rig, equipped with a modified T106 turbine blading and an upstream rotating vortex generator is considered and the numerical predictions are compared against hot film array measurements. In order to accurately assess both baseline transition and wake impact, simulations were conducted with unperturbed and periodically perturbed inflow conditions. Main mechanisms of transition and wake-boundary layer interaction are investigated utilizing a frequency-time domain analysis. Finally visualizations of the main flow structures and shear layer instabilities are provided utilizing the q-criterion as well as the finite-time Lyapunov exponent.

Effect of Tripping Laminar-to-Turbulent Boundary Layer Transition on Tip Vortex Cavitation

1997 ◽  
Vol 41 (01) ◽  
pp. 1-9
Author(s):  
T. Pichon ◽  
A. Pauchet ◽  
A. Astolfi ◽  
D. H. Fruman ◽  
J-Y. Billard
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Cross Section ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Tip Vortex ◽  
Layer Transition ◽  
Tip Vortex Cavitation

It is by now well established that, for Reynolds numbers larger than those corresponding to the conditions of laminar-to-turbulent boundary layer transition over a flat plate (≈0.5 × 106) and for a variety of wing shapes and cross sections, desinent cavitation numbers divided by the Reynolds number to the power 0.4 correlate with the square of the lift coefficient. In the case of foils having an NACA 16020 cross section and for Reynolds numbers below or close to those leading to transition over a flat plate, the results are very much different from those obtained for well-developed turbulent boundary layer conditions. Thus, a research program has been conducted in order to investigate the effect of boundary layer manipulation on cavitation occurrence. It consisted in determining the critical cavitation numbers, the lift coefficients, and the velocities in the tip vortex of foils having either a smooth surface or tripping roughness (promoters) near the leading edge. Tests were performed using elliptical foils of NACA 16020 cross section having the promoters extending over 60, 80 and 90 percent of the semi-span. The region near the tip was kept smooth in order to distinguish laminar-to-turbulent transition effects from tip vortex cavitation inhibition effects associated with artificial roughness at the wing tip. Results obtained at very low Reynolds numbers, ≥ 0.24 × 106, with the foil tripped on both the pressure and suction sides collapse rather well with those previously obtained at much larger Reynolds numbers with the smooth foil, and correlate with the square of the lift coefficient. The differences between the tripped and smooth foil results are due to the modification of the lift characteristics through the modification of the wing boundary layer, as shown by flow visualization studies, and as a result of the local tip vortex intensity.

CFD Prediction of Boundary Layer Transition and Separation on an Airfoil at Varying Angle of Attack

2007 ◽  
Author(s):  
Nicole M. Wolgemuth ◽  
D. Keith Walters
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Turbulent Airflow ◽  
Naca 0012

This study analyzes the predicted flow over a NACA 0012 airfoil at varying angles of attack and three different Reynolds numbers. The ability of three different turbulence models to predict boundary layer separation and transition behavior is investigated. Particular interest is paid to prediction of the separation bubble that develops near the leading edge of the airfoil suction surface prior to stall. The FLUENT CFD solver was used to simulate turbulent airflow over the airfoil. The three turbulence models include the standard and realizable forms of the k-ε model, available in FLUENT, as well as a recently developed transition-sensitive k-ω model that was implemented into the solver using user-defined functions. By employing the new, transition-sensitive model, computed properties of the flow field were found to be closer to experimental data than results produced by utilizing built-in turbulence models. Most importantly, the new, transition-sensitive model predicts the occurrence of the separation bubble, which the other models are unable to predict. The new model also clearly reproduces the laminar, transitional, and turbulent flow that occurs over the airfoil.

scholarly journals A comparison between aeroacoustic source mapping techniques for the characterisation of wind turbine blade models with microphone arrays

ACTA IMEKO ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 147
Author(s):  
Gianmarco Battista ◽  
Marcello Vanali ◽  
Paolo Chiariotti ◽  
Paolo Castellini
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Microphone Array ◽  
Wind Turbine Blade ◽  
Operating Conditions ◽  
Noise Sources ◽  
Aeroacoustic Noise ◽  
Array Measurements ◽  
Mapping Techniques ◽  
Acoustic Mapping

<p class="Abstract">Characterising the aeroacoustic noise sources generated by a rotating wind turbine blade provides useful information for tackling noise reduction of this mechanical system. In this context, microphone array measurements and acoustic source mapping techniques are powerful tools for the identification of aeroacoustic noise sources. This paper discusses a series of acoustic mapping strategies that can be exploited in this kind of applications. A single-blade rotor was tested in a semi-anechoic chamber using a circular microphone array. <br />The Virtual Rotating Array (VRA) approach, which transforms the signals acquired by the physical static array into signals of virtual microphones synchronously rotating with the blade, hence ensuring noise-source stationarity, was used to enable the use of frequency domain acoustic mapping techniques. A comparison among three different acoustic mapping methods is presented: Conventional Beamforming, CLEAN-SC and Covariance Matrix Fitting based on Iterative Re-weighted Least Squares and Bayesian approach. The latter demonstrated to provide the best results for the application and made it possible a detailed characterization of the noise sources generated by the rotating blade at different operating conditions.</p>

scholarly journals Effect of Surface Roughness on Boundary Layer Transition and Far Field Noise

2019 ◽  
Author(s):  
Qingqing Ye ◽  
Francesco Avallone ◽  
Daniele Ragni ◽  
Meelan M. Choudhari ◽  
Damiano Casalino
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Boundary Layer Transition ◽  
Far Field ◽  
Layer Transition ◽  
Field Noise ◽  
Effect Of Surface

scholarly journals Effect of Surface Roughness Geometry on Boundary-Layer Transition and Far-Field Noise

AIAA Journal ◽  
2021 ◽  
pp. 1-13
Author(s):  
Qingqing Ye ◽  
Francesco Avallone ◽  
Daniele Ragni ◽  
Meelan Choudhari ◽  
Damiano Casalino
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Boundary Layer Transition ◽  
Far Field ◽  
Layer Transition ◽  
Field Noise ◽  
Effect Of Surface

Experimental investigation of NACA-0012 airfoil instability noise with sawtooth trailing edges

2021 ◽  
pp. 0309524X2110605
Author(s):  
Basim Al Tlua ◽  
Joana Rocha
Keyword(s):  
Noise Reduction ◽  
Reynolds Numbers ◽  
Radiation Characteristics ◽  
Trailing Edge ◽  
Trailing Edges ◽  
Noise Measurements ◽  
Parametric Studies ◽  
Trailing Edge Serrations ◽  
Field Noise ◽  
Naca 0012

This study presents an experimental study of the effect of sawtooth trailing-edge serrations on airfoil instability noise. The far-field noise measurements are obtained to investigate the noise radiation characteristics of a NACA-0012 airfoil operated at various angles of attack: 0°, 5°, and 10°, and covered Reynolds numbers of 2.87 × 105, 3.71 × 105, and 5 × 105. It is found that as the Reynolds number increases, the instability noise shifts from tonal to broadband, whereas as the angle of attack increases, it shifts from broadband to tonal. Furthermore, sawtooth trailing-edges are used to minimize instability tonal noise, leading to considerable self-noise reduction. Parametric studies of the serration amplitude 2 h and streamwise wavelength λ are performed to understand the effect of sawtooth trailing-edges on noise reduction. It is observed that the sound pressure reduction level is sensitive to both the amplitude and streamwise wavelength. Overall, the sawtooth trailing-edge with larger amplitude and smaller wavelength produce the greatest amount of noise reduction.

Sign in / Sign up

Export Citation Format

Share Document