German-Dutch Wind Tunnel Research Articles

Highlights of the Lockheed Martin F-35 STOVL jet effects programme

AbstractThis paper presents the highlights of the F-35 STOVL Jet Effects (SJE) test effort during the complete four years of the System Development and Demonstration phase. A new 12%-scale F-35 SJE model was tested in the German-Dutch wind-tunnels Large Low Speed Facility in order to gather STOVL jet-induced Forces and Moments. Ten separate test entries were conducted, covering all STOVL flight regimes from pure hover in ground effect through transition to wing borne flight. This paper will present an overview of this program, including a detailed description of the wind-tunnel model, testing techniques, test conditions, and accomplishments.

Ground-Based Simulation of Complex Maneuvers of a Delta-Wing Aircraft

Ground-Based Simulation of Complex Maneuvers of a Delta-Wing Aircraft

Design and Testing of Low Noise Landing Gears

In the approach phase of large commercial aircraft, airframe noise – and in particular that from landing gears – is one of the dominant aircraft noise components. Within a European co-financed research project entitled “Significantly Lower Community Exposure to Aircraft Noise” (codenamed SILENCER) a study in “advanced low noise landing gear design” was performed to develop operational landing gears which take into account aeroacoustic constraints early in the design stage. Airbus aircraft typical configurations of low wing with underslung engines and A340 type gears were selected as reference. RANS flow field calculations were performed and used to identify and thus avoid the impingement of high speed flow onto critical gear structure elements. The evaluation of CFD results with respect to the effects on aerodynamic noise was performed on the basis of related experimental experience and a semi-empirical landing gear noise model. Both low noise advanced nose and main landing gears were designed and manufactured at full scale for noise testing in the 8 m by 6 m open test section of the German-Dutch Wind Tunnel (DNW-LLF).

Numerical Simulations of Fan Interaction Noise Using a Hybrid Approach

A source-to-far-field computation procedure aimed at predicting the noise generated by rotor-stator fan interactions is presented here. Interaction noise sources are assessed using a three-dimensional Reynolds-averaged Navier-Stokes (RANS) code. A modal expansion is applied to the computational fluid dynamics (CFD) data, and a source model is used to link the CFD to an Euler code simulating the acoustic propagation. Far-field noise is classically obtained by means of a Kirchhoff integral. The source model is detailed and validated over a selected benchmark. Then the hybrid method is applied to a turbofan model, tested in the German-Dutch Wind Tunnel. Simulations are compared to boundary element method computations previously performed and used here to validate the no-flow solution. Interacting cut-on mode amplitude deduced from CFD output postprocessing is adjusted to fit in-duct measurements on the outer wall. The predicted radiation field is related to the directivity patterns measured at several axial positions upstream of the fan inlet and fairly good agreement is found using the RANS/Euler/Kirchhoff procedure.

Recording and evaluation methods of PIV investigations on a helicopter rotor model

Three-component particle image velocimetry measurements at moderate speeds and observation distances can now be accomplished on a routine basis. This article discusses the experiment performed on a 4 m-diameter model rotor in the 6-m×8-m open test section of the Large Low Speed Facility of the German–Dutch Wind Tunnels. More than half a terabyte of raw data were recorded at various positions on the advancing and retreating sides of the rotor in order to obtain detailed measurements of the trailing vortex in the frame of an international project. This paper addresses measuring techniques and possible sources of errors and presents a limited number of cases for the purpose of illustrating the solutions to numerous technical challenges relating to the acquisition and analysis of vortical flows.

Optical measurement techniques for high Reynolds number train investigations

This article reports on experimental aerodynamic investigations on a generic high-speed train configuration performed within two different wind tunnels. Both wind tunnels are specialized facilities for high Reynolds number investigations and offer low turbulence levels. The wind tunnels are the cryogenic wind tunnel located in Cologne (KKK) and in the high-pressure wind tunnel located in Gottingen (HDG). Both facilities are part of the German–Dutch wind tunnel association (DNW). The adaptation and application of three optical measurement techniques for such high Reynolds number investigations is described in the article. The optical methods are: Particle Image Velocimetry for the measurement of velocity fields, Background Oriented Schlieren technique for density gradient measurements, and a white light Digital Speckle Photography technique for model deformation monitoring.

Rotor Wake Vortex Definition-Evaluation of 3-C PIV Results of the HART-II Study

An evaluation is made of extensive three-component (3-C) particle image velocimetry (PIV) measurements within the wake across a rotor disk plane. The model is a 40 percent scale BO-105 helicopter main rotor in forward flight simulation. This study is part of the HART II test program conducted in the German-Dutch Wind Tunnel (DNW). Included are wake vortex field measurements over the advancing and retreating sides of the rotor operating at a typical descent landing condition important for impulsive blade-vortex interaction (BVI) noise. Also included are advancing side results for rotor angle variations from climb to steep descent. Using detailed PIV vector maps of the vortex fields, methods of extracting key vortex parameters are examined and a new method was developed and evaluated. An objective processing method, involving a center-of-vorticity criterion and a vorticity “disk” integration, was used to determine vortex core size, strength, core velocity distribution characteristics, and unsteadiness. These parameters are mapped over the rotor disk and offer unique physical insight for these parameters of importance for rotor noise and vibration prediction.

Analysis of SPR measurements from HART II

The wind tunnel test of HART II (Higher Harmonic Control Aeroacoustic Rotor Test), performed in October 2001 in the Large Low-Speed Facility (LLF) of the German-Dutch Wind-tunnel (DNW), is part of an international cooperative program by the German DLR, French ONERA, DNW, NASA Langley and the US Army Aeroflightdynamics Directorate (AFDD). The main objective of the program is the investigation of rotor wake and its influence on rotor blade–vortex interaction (BVI) noise with and without higher harmonic pitch control (HHC). For blade position and deflection measurements the Stereo Pattern Recognition (SPR) technique was used for the first time. This technique is based on a 3-dimensional reconstruction of visible marker locations by using stereo camera images. An evaluation of these images leads to the spatial position of markers which are attached to each of the four blades and to the bottom of the fuselage and thus to the blade motion parameters in flap, lead-lag and torsion. In this paper the different analysis methods and post-processing of SPR data and the final results for all four rotor blades are presented and the advantages, drawbacks and the potential of this technology are shown.

Reynolds Number and Roughness Effects on Thick Airfoils for Wind Turbines

The effects of increased Reynolds number (Re) on clean and rough airfoils were investigated by wind tunnel experiments and by numerical simulation with an improved Navier-Stokes solver. By cooling the cryogenic wind tunnel in Cologne (KKK) of the German-Dutch Wind-Tunnel (DNW) down to 100 K, values of Re up to 10 × 106 were reached, based on a model chord of 500 mm. Whereas the clean surface configuration shows no drastic loss in maximum lift, the lift-to-drag ratio decreases from 95 to approximately 85, mainly due to an increase of drag. In contrast to that, rough surface configurations, including zig-zag tape for transition fixing and carborundum based distributed roughness around the nose, show increased performance for increased Re. In parallel, numerical simulations were carried out with a boundary layer stability code coupled to a Navier-Stokes solver. The trends in behaviour of the boundary-layer based properties were predicted well, in contrast to the separation pattern responsible for maximum lift.

Recording and evaluation methods of PIV investigations on a helicopter rotor model

Three-component particle image velocimetry measurements at moderate speeds and observation distances can now be accomplished on a routine basis. This article discusses the experiment performed on a 4 m-diameter model rotor in the 6-m×8-m open test section of the Large Low Speed Facility of the German–Dutch Wind Tunnels. More than half a terabyte of raw data were recorded at various positions on the advancing and retreating sides of the rotor in order to obtain detailed measurements of the trailing vortex in the frame of an international project. This paper addresses measuring techniques and possible sources of errors and presents a limited number of cases for the purpose of illustrating the solutions to numerous technical challenges relating to the acquisition and analysis of vortical flows.

Model and full scale high-lift wing wind tunnel experiments dedicated to airframe noise reduction

During landing approach, airframe noise has become a significant contributor to the overall radiated noise from commercial aircraft, when propelled by quiet high-bypass-ratio engines. The major sources of airframe noise are the landing gears and the wing high-lift devices (HLD). In view of European aviation industry to design and build a very large commercial aeroplane, the A3XX, a German National Research Project was initiated, culminating in a series of model- und full scale wind tunnel experiments on HLD. This paper discusses recent results from HLD-studies in the German Dutch Wind Tunnel (DNW) on a 1/7.5 scaled complete model aircraft and the outer section of an A320 full scale wing, employing farfield microphones, unsteady pressure instrumentation and source localization techniques to quantify airframe noise levels and identify the major aeroacoustic sources. The tests provided a baseline data set for the development of noise prediction schemes. Test results obtained on the full scale wing section revealed the importance of excess noise from construction details of a real wing HLD. Tonal components in scale model flap side-edge surface pressure spectra were found to originate from scale model Reynolds number effects. The acoustic effectiveness of initial noise reduction concepts was assessed.

ヘリコプタのブレード/渦干渉騒音の解析

Two types of prediction tools for helicopter noise have been developed under the cooperative research between Advanced Technology Institute of Commuter Helicopter Ltd. (ATIC) and National Aerospace Laboratory (NAL) . One of them is a combined method of CAMRAD II, interpolation code for blade motion and wake geometry, aerodynamic code of 3D unsteady Euler solver, and aeroacoustic code based on Ffowcs Williams and Hawkings (FW-H) formulation. The other consists of CAMRAD II, 3D unsteady Euler solver using moving overlapped grid method, and FW-H code. The acoustic waveform of Blade-Vortex Interaction (BVI) noise predicted by the former tool is in good agreement with the experimental data of 1/7-scale model AH-1 Operational Loads Survey (OLS) rotor. This method is applied to investigate the effect of blade-tip shape on the intensity of BVI noise. As a result, it is shown that anhedral and swept-forward tip shapes effectively reduce the BVI noise of OLS rotor in a descent flight condition. The predicted Effective Perceived Noise Level (EPNL) of a helicopter is also compared with the experimental data obtained by ATIC and reasonable correlation is obtained. The latter tool successfully predicts the distinct spikes in the BVI wave-form of ATIC model rotor tested in German-Dutch Wind Tunnel (DNW) . In the comparison of measured and calculated carpet noise contours, reasonable agreement is obtained. The present tools are expected to be useful for the design of low-noise helicopters in the future.

European helicopter rotor noise research—Highlights of recent projects

Significant advances in understanding, modeling, and controlling helicopter rotor noise have been made in the course of several major European rotor aeroacoustic research projects over the past years. The availability of the German–Dutch Wind Tunnel (DNW), in particular, has enabled research on relatively large main rotor models (up to typically 40% full scale). Here, the simultaneous application and use of blade-mounted absolute pressure sensors to study the very aeroacoustic source mechanisms, of advanced acoustic-data acquisition systems for the radiated noise, of non-intrusive flow visualization as well as flow and blade deflection measurement techniques to investigate the rotor wake and the blade dynamic response has provided much insight into the physics of rotor aeroacoustics, particularly into the rotor blade-vortex interaction (BVI) impulsive noise phenomenon. In efforts towards controlling BVI impulsive noise, in some research projects, active blade-root control techniques have been investigated to favorably affect the BVI geometry and thus minimize the impulsive noise radiation. Much of the experimental data acquired served as benchmark information to enhance the mathematical modeling of the rotor wake, the rotor airloads, and the noise radiation. In this lecture, several major European helicopter aeroacoustic research projects are discussed.

HHC aeroacoustic rotor tests in the German-Dutch wind tunnel: Improving physical understanding and prediction codes

Within an international research program jointly conducted by the US Army's Aeroflightdynamics Directorate (AFDD), NASA Langley, DNW, ONERA and DLR, the effects of a higher harmonic blade pitch angle variation on the rotor noise and vibrations were intensively studied. The program, denoted with Higher Harmonic Control Aeroacoustic Rotor Tests (HART) comprised both theoretical and experimental activities, the latter ones being represented by a comprehensive wind tunnel test campaign. Besides aeroacoustic measurements it comprised flow visualization tests and flow field measurements which were applied along with optical methods to determine the blade deflections. The measurements were preceded by extensive predictions performed with the analytical models of each organization. Within these simulations different models were used, leading to a very comprehensive theoretical data base. It gave an impression of the rotor codes' uncertainties which were tried to be eliminated by means of the wind tunnel findings. Although these activities yielded general improvements of the simulation codes they demonstrated also that further work is required in order to accurately predict the effects of a higher harmonic blade pitch angle on the rotor noise and vibrations.

Key Results From a Higher Harmonic Control Aeroacoustic Rotor Test (HART)

In a major cooperative research program within existing US-German and US-French Memoranda of Understandings (MoU's) a comprehensive experimental study was conducted with a 40-percent geometrically and dynamically scaled BO-105 main rotor operated in the open-jet-anechoic test section of the German-Dutch Wind Tunnel (DNW). The objectives of the program were to improve the physical understanding and the mathematical modelling of the effects of the higher harmonic blade pitch control technique on blade-vortex interaction (BVI) impulsive noise and vibration reduction. A unique set of acoustic, dynamic, dynamic response, performance, and rotor wake data were acquired with a pressure and strain gauge instrumentedblade and by application of non-intrusive measurement techniques. This paper is focused on the experimental part of this research program, termed Higher-harmonic-control Aeroacoustic Rotor Test (HART) which was jointly performed by researchers from the.

Analysis of helicopter blade vortex structure by laser velocimetry

In descent flight, helicopter external noise is mainly generated by the Blade Vortex Interaction (BVI). To under-stand the dynamics of this phenomenon, the vortex must be characterized before its interaction with the blade, which means that its viscous core radius, its strength and its distance to the blade have to be determined by non-intrusive measurement techniques. As part of the HART program (Higher Harmonic Control Aeroacoustic Rotor Test, jointly conducted by US Army, NASA, DLR, DNW and ONERA), a series of tests have been made in the German Dutch Wind Tunnel (DNW) on a helicopter rotor with 2 m long blades, rotating at 1040 rpm; several flight configurations, with an advance ratio of 0.15 and a shaft angle of 5.3°, have been studied with different higher harmonic blade pitch angles superposed on the conventional one (corresponding to the baseline case). The flow on the retreating side has been analyzed with an especially designed 3D laser velocimeter, and, simultaneously, the blade tip attitude has been determined in order to get the blade-vortex miss distance, which is a crucial parameter in the noise reduction.

Acoustics of a counter-rotating shrouded propfan - Prediction and data

The acoustic characteristics of a counter-rotating integrated shrouded propfan are studied both theoretically and experimentally. The calculation method comprises the main noise generation mechanisms of the propulsor as steady rotor blade loading noise, rotor/rotor and rotor/struts interaction noise, inlet flow distortion noise, and broadband noise. It accounts for flow, duct, and blade sweep effects, sound reflection from the blade rows, and propagation through inlet and nozzle. The calculation model is verified by measurements taken with a 0.4m-diam, air turbine driven propfan model with 10 blades on each of the two rotors in the German-Dutch Wind Tunnel DNW. Deviations between calculated and measured results are attributed to mode and frequency conversion effects occurring when the sound from the rear rotor is reflected from the front rotor and when it is transmitted through the struts. A parametric study showed that the frequency and directivity characteristics of the sound field of a fan with slightly different blade numbers on both rotors are similar to those of a fan with equal rotor blade numbers. Both blade sweep and tip speed have a small influence on far-field noise, but a considerable influence on cabin noise, according to the calculation. Takeoff far-field noise can be reduced by increasing the axial distance between the rotors.

Comparative measurements in the canonical boundary layer at Reδ2≤6×104 on the wall of the German–Dutch windtunnel

Mean velocity and Reynolds-stress profiles were measured in the incompressible turbulent boundary layer with zero pressure gradient on the aerodynamically smooth sidewall of the German–Dutch windtunnel. Data were taken at Reynolds numbers Reδ2, based on momentum thickness δ2 of 2×104, 4×104, and 6×104 by means of four different types of hot-wire probes (three-wire probes, X wire, and normal-wire probes). There are also measurements of skin friction and of spectra. The data compare well with the few available other measurements, and all profiles show independence of Reynolds number in the outer region of the boundary layer when plotted against y/Δ, where Δ is the Rotta–Clauser length.

Wall interference correction to drag measurements in automotive wind tunnels

A low-order panel method has been devised for calculating wall interference corrections to the measured drag force in automotive wind tunnels with closed, 34-open or slotted-wall test sections. The method is applied to the Motor Industry Research Association (MIRA) generic car model, tested in three working sections of the German-Dutch Wind Tunnel (DNW), and to three subscale models tested in the DSMA closed-circuit pilot wind tunnel with closed and slotted walls. The calculations show that the drag measurements in closed test sections and 34-open test sections require negative and positive corrections, respectively, whereas inside a test section with 30% open longitudinally slotted walls the measurement is nearly interference-free.

Experimental Results of the European HELINOISE Aeroacoustic Rotor Test

In a cooperative research program between eight European partners, a 40% geometrically and dynamically scaled and highly instrumented model of the ECD (formerly MBB) BO 105 helicopter main rotor was tested in the open-jet anechoic test section of the German-Dutch Wind Tunnel (DNW) in the Netherlands. The primary objectives of this experimental study were 1) to improve the physical understanding of the impulsive rotor noise sources by correlating blade pressure and acoustic characteristics and 2) to provide an extensive airload and acoustic database for code validation purposes.Consequently, a comprehensive set of simultaneous acoustic and aerodynamic blade surface pressure data as well as blade dynamic and performance data were measured for the standard rotor with rectangular blade tips. In addition, initial quantitative information of the blade- vortecx miss distance during blade-vortex interaction (BVI) was obtained.