Wind Tunnel Wall Interference Research Articles

Wind tunnel wall interference correction for transonic airfoils with data-reduced ensemble Kalman filter

The uncertain factors in wind tunnel experiments, especially the interference effects, will cause the flow around the test model to differ from that under the free flow condition. The wind tunnel wall interference effects are challenging to be eliminated, especially in transonic flow regions where classical linear correction methods are ineffective. To address this issue, an efficient wind tunnel wall interference correction framework based on data assimilation is proposed for steady and shock buffet flows around the airfoils in the transonic region in this work. The ensemble Kalman filter (EnKF) is used to find the combination of inflow conditions, which minimizes the differences between the pressure coefficients measured in the wind tunnel experiment and those estimated by computational fluid dynamics (CFD). The polynomial chaos expansion method is used to propagate uncertainty in the forecast step of the EnKF in order to improve efficiency. Typical wind tunnel wall interference correction problems are studied, including two steady cases: the transonic flow around the Royal Aircraft Establishment 2822 (RAE2822) and the National Aerospace Laboratory 7301 (NLR7301) airfoils, and one unsteady case: the transonic shock buffet on the National Aeronautics and Space Administration supercritical (phase 2)-0714 (NASA SC(2)-0714) airfoil. It is demonstrated that with the corrected Mach number and angle of attack, the estimated CFD results are in better agreement with the measured experimental data than traditional linear methods and the computational efficiency is improved compared to the original EnKF.

Evaluation of wind tunnel wall interference using homogeneous and measured boundary conditions

The experimental results obtained in a wind tunnel must be subjected to a correction process which aims to eliminate the influence of the limited dimensions of the flow field around the model. This is necessary because the results must be independent of the characteristics of the laboratory where they were obtained, in order to ensure the quality of the parameters.The wall corrections are applied to the global quantities that characterize the undisturbed flow, such as the Mach number or the dynamic pressure, but they are also applied to the quantities related to the model, namely the global aerodynamic coefficients.Consequently the corrections will be applied to the global quantities of the undisturbed flow and therefore they will be transmitted to the aerodynamic quantities related to the model.

Methods of the wall interference reduction at low supersonic velocities in wind tunnels

The paper describes the research aimed at reducing wall interference in wind tunnels at low supersonic velocities. The results of such wind tunnel tests are often affected by wave perturbations generated by the model and reflected from the test section walls. This research describes the methods that can effectively reduce the wave reflection from the wall. A numerical investigation is presented that includes a novel boundary condition that eliminates disadvantages of previously considered methods. The numerical study was conducted in the frame of electronic wind tunnel concept and ANSYS CFX software. The numerical investigation showed that the effect of shock wave reflection could be reduced using a new type of boundary condition that is a combination of perforated walls and a controlled boundary layer.

Nonlinear Wind-Tunnel Wall-Interference Corrections Using Data Assimilation

This paper presents a novel approach for correcting wind-tunnel wall interference in the nonlinear flow regime, that is, in the presence of phenomena such as flow separation and shocks. The methodology uses a gradient-based optimization to minimize the difference between experimental measurements and a Favre-averaged Navier–Stokes (FANS) simulation. The aim is to exploit the high-fidelity experimental data to correct turbulence-modeling errors in the FANS simulations, as well as to use the accurate angle of attack and Mach number from the FANS simulations to correct the in-tunnel flow conditions. The optimization is carried out directly in free air, thus avoiding the requirement to mesh the wind-tunnel walls and/or to model the ventilated-wall boundary condition. A byproduct of this method is the availability of flow information everywhere around the test object, which augments and complements the experimental data. The methodology is tested on two-dimensional and three-dimensional flow cases, demonstrating a significant improvement in the agreement between experimental and numerical data.

Wall Interference Correction Method for Kevlar Wall Test Section

This Paper describes a new method of correcting the wind tunnel wall interference of permeable Kevlar test section walls. The classical three-dimensional panel method is extended to flows in a Kevlar-walled test section and modified to improve its general predictability. The results computed using this enhanced panel method are in good agreement with experimental results with regard to the pressure distributions on a wind tunnel model and Kevlar wall surfaces and the Kevlar wall deformation. With this new tool, which can compute flows in a Kevlar-walled wind tunnel precisely, it is possible to compute the disturbance flows due to the walls correctly and separately from those due to the wind tunnel model. The effects of the wind tunnel walls on blockage and downwash of the flow in the wind tunnel are estimated by calculating the disturbance flow velocity due to the walls at the model reference point. Wall interference corrections using this new method are applied to a high-lift semispan wing model installed in a Kevlar-walled test section, and the results demonstrate that the method is practicable and reliable.

Application of combined jet-perforated boundaries to solve the problem of the wind tunnel wall interference at transonic speeds

Application of combined jet-perforated boundaries to solve the problem of the wind tunnel wall interference at transonic speeds

Analyzing the effect of wind tunnel wall on the aerodynamic performance of airfoils

This paper analyzes the effect of wind tunnel wall interference on the airfoil aerodynamic performance, based on the results of experiment and CFD numerical simulation. The experimental measurement was made in IET using the low-speed and closed wind tunnel. The airfoil was DU91-W2-250. The numerical simulation with tunnel wall (wall), without tunnel wall (no wall) and without side tunnel wall (no side wall) were performed. Through the comparison the results between Exp and CFD, it is feasible to use CFD numerical simulation in this paper. And we get the following conclusions: the upper and lower tunnel walls make the flowing area decrease and the velocity increase due to the thickness of boundary layer on the walls, and they also casuse that C l and C d increase. The side tunnel walls cause span-wise flowing and delay the flow separation on the surface of airfoil, meanwhile, they cause that the velocity decreases, C l decreases and C d increases. At small angles of attack, the effect of side tunnel walls on the flowing of airfoil surface can be neglected. However, this effect is very significant at large angles of attack. The classical method can not work well at large angle of attacks for the correction of wall interference in wind tunnel because it doesn’t consider the effect of tunnel wall boundary layer. The C l should be increased through the correction, meanwhile, it is found that the flowing is not two-dimensional flow at large angles of attack in the free-air condition, so we suggest that the pressure measurement with more cross sections or using balance method should be used to obtain the aerodynamic performance of airfoil.

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

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

280 風洞壁干渉補正に対するデータ同化の適用と課題

280 風洞壁干渉補正に対するデータ同化の適用と課題

Dynamic test experiment system of single degree of freedom of Φ3.2 m wind tunnel

Post-stall maneuverability is a key technical indicator for modern fighter. It requires a fighter to maintain excellent dynamic behaviors at a high angle of attack. The dynamic stability derivative is a design input off light control system and one of its important sources is the wind tunnel test. In order to meet stricter quality requirements of test data, China Aerodynamics Research & Development Center (CARDC) has set up a forced oscillation dynamic test system based on single degree of freedom in the open test section of Φ3.2 m wind tunnel. Based on the electronic cam, in this system, the servo motor-decelerator directly drives the supporting rod. The system simplifies the structure of device, reduces the number of moving parts as well as the mechanical clearance. Features of the system include: (1) a large variation range of frequencies and amplitudes, a higher control precision and step-less regulation; (2) independent variation of angle of attack and sideslip angle so that the combination of angle of attack and sideslip angle can be more convenient with higher test efficiency; (3) a small wind tunnel wall interference and support interference. Same set of devices can enable small amplitude dynamic derivatives test, large amplitude oscillatory test, and static force measurement, all of which contribute to a consistent measurement basis. With this test system, we developed a simplified fighter model dynamic test, obtaining dynamic derivatives and unsteady aerodynamic loads. Results of our tests verified the rationality and reliability of data as well as a high precision of repeatability.

Experimental Study of the Plunging Motion with Unsteady Wind Tunnel Wall Interference Effects

A series of experiments were carried out to investigate unsteady behavior of the flow field as well as the boundary layer of an airfoil oscillating in plunging-type motion in a subsonic wind tunnel. The measurements involved surface-mounted hot films complimented with surface pressure. In addition, wind tunnel wall pressure distribution was acquired to furnish a baseline for the wall interference corrections. The airfoil is the section of a 660-kW wind turbine blade. The experiments were conducted at a Reynolds number of 0.42 million, and over two reduced frequencies of k = 0.06 and 0.085, at prestall, nearstall, and poststall regions. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. The plunging displacements were transformed into the equivalent angle of attack. The surface hot-film measurements provided information about the boundary-layer events. The boundary-layer transition occurred via a laminar separation bubble. Variations of the surface pressure coefficients and aerodynamic loads with the equivalent angle of attack showed strong sensitivity to the reduced frequency and the mean angles of attack. The wall pressure distribution was affected by the model oscillation especially the region underneath the model.

Aerodynamic Characteristics of Bodies of Revolution at Near-Sonic Speeds

pressure distributions, drag, and flow characteristics around a family of sting- mounted truncated parabolic bodies of revolution at near-sonic and low-supersonic speeds by comparisons with an extensive existing wind-tunnel database. The analyses included both inviscid and viscous coupled boundary layer analyses. The investigations also included assessments of wind-tunnel wall interference effects as influenced by the various body geometries and test conditions. Extensive test versus theory comparisons of surface pressure distributions, flowfield pressures, anddrag forces are presented for subsonic through low-supersonic Mach numbers for the family of test configurations. An additional objective of these studies was to demonstrate the value of using existing and even rather historic experimental data. The experimental data used in the current studies were obtained from NACA wind-tunnel tests reported in 1958. ECENT near-sonic and low-sonic boom transport aircraft development studies have sparked a renewed interest in the natureoftheaerodynamicsaboutconfigurationsdesignedtocruiseat near-sonic or low-supersonic speeds. The validity of both the wind- tunnel test facilities and the computational methods are challenged by the characteristics of the flow at near-sonic speeds. The flow disturbances induced by a configuration at near-sonic and low- supersonic speeds extend to very large lateral distances. This presents a significant challenge to obtain interference-free wind- tunnel test data and also greatly increases the required lateral extent of the typical computational domain. Consequently, a number of fundamental aerodynamic studies were conducted to assess the ability of the TRANAIR full potential code to predict pressure distributions, drag, and flow characteristics around a family of sting-mounted truncated parabolic bodies of revolution at near-sonic and low-supersonic speeds by comparisons with an extensive existing wind-tunnel data base (1,2). The analyses includedbothinviscidandviscouscoupledboundarylayeranalyses. The investigations also included assessments of the effects of wind- tunnelwallinterferenceasinfluencedbythevariousbodygeometries and test conditions. The physics of the actual flow characteristics separating behind a truncated body and flowing onto a support sting are not correctly modeled by inviscid computational fluid dynamics (CFD) methods which typically include a constant area wake equal to the base area that trails behind the body. Using an analogy between the separated flowfromtheaftbodytothestingandthatofseparated flowbehinda backward facing step, a simple representation of the wake shape was developed and implemented in the TRANAIR analyses. The total drag for each configuration included the pressure drag obtainedbyintegrationofthepressuredistributions,plustheviscous drag. For the inviscid analyses, the viscous drag was estimated by using flatplateskinfrictiontheory.Theviscousdragestimatesforthe coupled boundary layer viscous analyses were obtained by integration of the calculated local skin friction distribution over the surface area of each body. This report presents the results of the subsonic, near-sonic, and supersonic investigations. An additional objective of these studies was to demonstrate the value of using existing and even rather historic experimental data. The experimental data usedin the current studies were obtained from NACA wind-tunnel tests reported in 1958. The study reported in this paper illustrates a process of using the essential tools of the aerodynamist shown in Fig. 1. These tools include computational fluid dynamics (CFD), experimental fluid dynamics (EFD), simplified fluid dynamics (SFD), visual fluid dynamics (VFD), and the most important tool of all, understanding fluid dynamics (UFD).

Analysis of Wind Tunnel Wall Interference Effects on Subsonic Unsteady Airfoil Flows

In this work, the effect of wall interference on steady and oscillating airfoils in a subsonic wind tunnel is studied. A variety of approaches including linear theory, compressible inviscid and viscous computations, and experimental data are considered. Integral transform solutions of the linearized potential equations show an augmentation of the lift magnitude for steady flows when the wall is close to the airfoil surface. For oscillating airfoils, lift augmentation is accompanied by a significant change in the phase of the lift response. Idealized compressible Euler calculations are seen to corroborate the linear theory under conditions that are sufficiently away from acoustic resonance. Further, the theory compares well with compressible Reynolds-averaged Navier-Stokes calculations and experimental measurements over a wide range of attached flows at subsonic Mach numbers. The present methodology can thus be used to predict wall interference effects and also to help extrapolate linear and nonlinear (dynamic stall) wind tunnel data to free-air conditions.

Wall Correction Model for Wind Tunnels with Open Test Section

In the paper we present a correction model for wall interference on rotors of wind turbines or propellers in wind tunnels. The model, which is based on a one-dimensional momentum approach, is validated against results from Navier–Stokes computations using a generalized actuator disc principle. In the model the exchange of axial momentumbetweenthetunnelandtheambientroomisrepresentedbyasimpleformula,derivedfromactuatordisc computations. The correction model is validated against Navier–Stokes computations of the flow about a wind turbine rotor. Generally, the corrections from the model are in very good agreement with the computations, demonstrating that one-dimensional momentum theory is a reliable way of predicting corrections for wall interference in wind tunnels with closed as well as open cross sections.

On Boundary Conditions Modelling of the Fluid‐Structure Interaction at Wind Tunnel Testing

AbstractThe present paper discusses some newer developments, but concentrates mainly on the specification of the wall boundary conditions that are of importance for the calculation of the wind tunnel wall interference. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental and numerical Investigation of wind tunnel wall interference near Mach one

Surface pressure measurements on the CAST-10-2/DOA 2 aerofoil, conducted in the IAR l.5m wind tunnel and supported by CFD simulations, are used to validate some new theoretical analyses of transonic wall interference. Based on the transonic freeze principle, it is shown that the stream Mach number correction is indeterminate near Mach one.

Numerical and experimental investigations on the reduction of wind tunnel wall interference by means of adaptive slots

AbstractThe flow in many wind tunnel experiments is affected by the presence of test section walls. The resulting interference can be minimised by correcting the measured model pressures, or by influencing the model flow directly with the use of ventilated or adaptive test section walls. The objective behind the latter technique is to guide the flow in the test section to achieve low interference (i.e. free flow) condition at the model. The most successful technique of flexible, adaptive walls is still restricted to small research wind tunnels due to its mechanical complexity. However, a very promising alternative is the use of adaptive slots in the test section walls. This concept combines the method of passive slotted walls, as they are already implemented in many large wind tunnels, and flexible walls. Additionally, this technique presents the opportunity of full 3D adaptations because the slots can be situated in all four test section walls.This paper presents preliminary experimental results and the latest numerical calculations on the effectiveness of adaptive slots. The experiments were conducted under high subsonic flow conditions in the new slotted test section of the transonic wind tunnel at TU Berlin’s Aeronautical Institute (ILR).The numerical results presented are focussed on the 2D slot adaptation of a 2D-model (CAST7 aerofoil) and the 3D slot adaptation of a body of revolution (3D-ETB). In addition, basic studies were made of the flows associated with a single slot on one wall and a bump on the other.The numerical and the first experimental investigations have shown the potential of adaptive slots to reduce wall interferences effectively. The adaptation accuracy of the investigated slot configurations deviated not more than 3% from the reference case (2D-wall adaptation).

Correction of Wall Interference in Wind Tunnels: A Numerical Investigation

A procedure is described for the correction of wind-tunnel wall interference effects on the experimental measurement of aerodynamic coefficients. The correction is given by the difference between the values obtained in two different numerical simulations: In the first one the flow over the model in free-air conditions is simulated, whereas in the second one, the measured pressure values over the wind tunnel walls are used as boundary conditions. A necessary preliminarly step is the choice of the number, location, and accuracy of the pressure measurements. A strategy is proposed to determine these parameters, based on the same correction procedure in which the experimental part is replaced by numerical simulation. This strategy is applied to the subsonic flow around a complete aircraft configuration by means of a potential flow solver. The sensitivity to the number and location of sensors, as well as to the transducer accuracy, is investigated. Given the desired correction accuracy, the proposed strategy permits identification of suitable configurations with reduced time and computational costs

Numerical simulation of wind tunnel wall effects on wind turbine flows

A low-order panel method and a prescribed wake vortex model have been combined into a coupled model capable of assessing the basic effect of wind tunnel walls on wind turbine flow and performance. The wind tunnel walls are discretised into a series of panels, and sources distributed on these panels simulate the constraint effect of the wind tunnel walls. The wind turbine and its wake are represented by the prescribed wake model. The source strengths are related to the induced velocities at the panel control points due to the turbine vortex system by satisfying the boundary condition of zero normal velocity on the solid tunnel wall. The vortex-induced and source-induced velocities at the blade are summed to determine an interim turbine wake using the prescription functions. The effects of the disturbance velocities due to the source panels are then superposed upon the prescribed wake to obtain the final wake geometry under the influence of wind tunnel wall interference. The model developed in this study is compared with wind turbine wake measurements made in a low-speed wind tunnel. Generally, the model is found to compare well with experiment, although some discrepancies are noted. Finally, possible future improvements to the combined method are recommended. Copyright © 2001 John Wiley & Sons, Ltd.

Recent experience in the prediction and assessment of windtunnel wall interference

AbstractRecent experience in the prediction and assessment of windtunnel wall interference is reviewed. Three areas of development are identified. The first deals with the influence of wall boundary layers on wall-induced velocities in solid-wall windtunnels; the second is concerned with preparations for determining wall interference in the European Transonic Windtunnel and the third relates to recent studies aimed at providing the basis for correcting data to free-air conditions.