Application of the fast Fourier transform to two-dimensional wind tunnel wall interference

To analyze wall interference of a transonic wind tunnel, flows of two-dimensional airfoil with wind tunnel porous walls are computed by CFD and the new porous wall model. First, the computational results are validated by comparing with measurement. The porous wall model shows high accuracy enough to precisely simulate the wall interference. Effect of the wall interference is discussed by comparing two kinds of computational results with and without the wind tunnel wall. Wall interference by the porous wall is characterized by the downwash and blockage. Porous wall is effective for decreasing the blockage, which causes the acceleration around the airfoil. However, high porosity of the porous wall causes the large downwash, and it changes incidence angle of the airfoil. The Mokry's correction method for wall interference is verified by applying the correction to CFD results. The Mokry's method shows high accuracy in subsonic and no stall conditions, which meet the requirement of small perturbation potential equation. The accuracy is also high even if the model is large relative to the wind tunnel size. However, about 10 drag count error is caused under the transonic flow. The accuracy is rapidly reduced around the stall condition, and over 100 count error is caused. Nomenclature= coordinate = velocity of x,y direction = flow angle ( ( )) [deg] = lift coefficient = drag coefficient = height of wind tunnel = chord length of airfoil = airfoil thickness = porosity (ration of hole to wall area) = angle of attack

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“…A detail formulation of Mokry's method can be found in ref. 1. Correction values of Mach number and angle of attack are calculated from .…”

Section: A Mokry's Methodsmentioning

confidence: 99%

“…Currently, accuracy required for the measurement is less than 1 drag count error ( ), and therefore it is a key issue how to remove the wall interference. Several correction methods for the wall interference have been proposed before [1][2][3][4] . Many of these correction methods are based on the small perturbation potential equation.…”

Section: Introductionmentioning

confidence: 99%

Numerical Analysis of Wind Tunnel Wall Interference on Two-dimensional Airfoil by New Porous Wall Model

Nambu

Hashimoto

Murakami

et al. 2012

30th AIAA Applied Aerodynamics Conference

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“…Measured pressure distribution over walls is used as a boundary condition for the potential flow solution within test section. Mokry [4] used fast Fourier transformation to solve Laplace equation in twodimensional wind tunnel test section, using experimental wind tunnel wall pressure distributions combined with a doublet -vortex approximation of the airfoil shape as boundary conditions to solve Laplace's equation. The intensity of the vortex is adjusted to the measured lift coefficient, while corrections are made on angle of attack and airspeed due to buoyancy effect.…”

Section: Overview Of Different Correction Methods Approachesmentioning

confidence: 99%

Two-dimensional wind tunnel measurement corrections by the singularity method

Abdullah

2015

Teh. vjesn.

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Original scientific paper The correction method for pressure coefficient distribution around an airfoil is developed for the purpose of the postprocessing of wind tunnel data, obtained from the model pressure measurements. Pressure coefficient distribution around the airfoil, directly obtained by wind tunnel measurements, is corrected numerically in order to compensate for the interference effects of the wind tunnel test section walls. In this paper, the airfoil NACA0012 is approximated by linear vortex segments, which are then mirrored using sufficient number of images with respect to the ceiling and the floor of the test section, to model the flow pattern around an airfoil in the wind tunnel test section with solid walls. Flow calculations, both with the tunnel wall presence and in the free stream, are then performed. The numerically obtained pressure coefficient difference between these two cases should be superimposed to the pressure coefficient distribution measured in the wind tunnel, for the same nominal airflow parameters and angle of attack, at the corresponding points, resulting in the corrected experimental pressure coefficient distribution. The values of corrections generally increase with the reduction of the wind tunnel test section relative height. The paper is focused on the verification of lift curve slope corrections, where very good agreements have been obtained with several well-known classical correction methods. Keywords: pressure coefficient; singularity method; vortex distribution; wall interference; wind tunnel corrections Korekcije rezultata dvodimenzijskih aerotunelskih mjerenja metodom singularitetaIzvorni znanstveni članak Razvijena je metoda za korigiranje raspodjele koeficijenta pritiska oko aeroprofila u cilju obrade rezultata dobivenih mjerenjima pritiska na modelu u aerotunelu. Zbog utjecaja interferencije sa zidovima radnog dijela aerotunela, raspodjela koeficijenta pritiska neposredno dobivena mjerenjima korigira se numerički. U ovom radu, aeroprofil NACA 0012 aproksimiran je linijskim vrtložnim segmentima, koji se preslikavaju kao lik u ogledalu dovoljno puta u odnosu na položaje poda i plafon radnog dijela, da bi se modeliralo strujanje oko aeroprofila u neporoznom radnom dijelu aerotunela. Proračun se zatim vrši kako za slučaj strujanja sa prisustvom zidova, tako i za opstrujavanje u slobodnoj atmosferi. Razlika u numerički određenoj raspodjeli koeficijenata pritiska za ova dva slučaja se u odgovarajućim točkama superponira sa raspodjelom pritisaka izmjerenom u aerotunelu, pri istim nominalnim uslovima strujanja i napadnom uglu, čime se dobija korigirana eksperimentalna raspodjela pritisaka. Koeficijent uzgona se zatim izračunava iz tako korigirane raspodjele koeficijenata pritiska. Vrijednosti korekcija generalno rastu sa smanjenjem relativne visine radnog dijela aerotunela. Rad je fokusiran na verifikaciju faktora korekcije gradijenta uzgona, gdje su vrlo dobra poklapanja dobijena u usporedbi s nekoliko poznatih klasičnih metoda korekcije.

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“…Many wall interference correction methods are based on this equation. 22,23) The linearized small perturbation potential equation for wall interference correction can be written as:…”

Section: Evaluation Of Interference Quantitymentioning

confidence: 99%

Numerical Analysis of the ONERA-M6 Wing with Wind Tunnel Wall Interference

Nambu

Hashimoto

Aoyama

et al. 2015

Trans. Japan Soc. Aero. S Sci.

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The flow around an ONERA-M6 wing, including the effect of wind tunnel wall interference, is computed using CFD analysis with a porous wall model. The computational domain sets porous walls at the top and bottom of the wing section similar to actual wind tunnel experiments. The computational result captures almost the same shock wave shape as the wind tunnel. This could not be computed exactly in previous works that did not include wall effects. The interference of the porous walls reduces the Mach number and attack angle of the flow, and these effects alter the swept angle of front shock wave and the location of rear shock wave. The aerodynamics coefficients are also affected by the wall interference. The lift coefficient becomes smaller due to the reduction in attack angle. The lower Mach number decreases the drag coefficient, while the reduction in attack angle causes additional drag by a mechanism similar to induced drag.

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Application of the fast Fourier transform to two-dimensional wind tunnel wall interference

Cited by 47 publications

References 8 publications

Numerical Analysis of Wind Tunnel Wall Interference on Two-dimensional Airfoil by New Porous Wall Model

Numerical Analysis of Wind Tunnel Wall Interference on Two-dimensional Airfoil by New Porous Wall Model

Two-dimensional wind tunnel measurement corrections by the singularity method

Numerical Analysis of the ONERA-M6 Wing with Wind Tunnel Wall Interference

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