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Schepers, J.G. (author), Oerlemans, S. (author), Guidati, G. (author), Wagner, S. (author)The objective of the European project DATA (Design and Testing of Acoustically Optimized Airfoils for Wind Turbines) is a reduction of trailing-edge (TE) noise by modifying the airfoil shape and/or the application of trailing-edge serrations. This paper describes validation measurements that were performed in the DNW-LLF wind tunnel, on a model...report 2001
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Sijtsma, P. (author)A theory is presented to calculate acoustic modes in a circular flow duct lined with porous material. The porous material is divided into annular segments by a rigid structure, which prevents axial sound propagation from one segment into the other. Single modes cannot exist in such a configuration, but it is shown that approximate solutions of...report 1996
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Noback, R. (author)A method is described to generate a random Gaussian process with a power spectrum with fractional power, for example the von Karman spectrum for atmospheric turbulence. The method uses digital filtering of a white noise process and it is based on the use of fractional derivatives. An algorithm to generate the process is presented.report 1988
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Zandbergen, T. (author)An experimental investigation was carried out in the low speed wind tunnel LST to study aircraft engine noise generation by rotor/stator interaction. Reported is a follow-up experiment including detailed acoustic measurements in the duct downstream of a rotor with cylindrical pins to complement earlier tests whereby rotor wake velocities and...report 1987
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- Pietersen, O.B.M. (author), Klinker, F. (author), Roefs, H.F.A. (author), Lucas, A.M.G.M. (author) report 1984
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Prins, J.J.M. (author)Torque and force irregularities of running reaction wheels were studied. In this first part of the study report results from noise measurements at constant wheel speeds on various types of current technology European reaction wheels, both with ball- and magnet bearings and with DC or AC drive motor, are presented. The measured noise in radial...report 1982
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Prins, J.J.M. (author)The increasing power of on-board processors allows more freedom in the design and operation of reaction wheel control systems. This report discusses several performance and implementation aspects of the operation of wheel systems which have their own internal feedback control system. A model following control concept is found to be superior. The...report 1982
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Pietersen, O.B.M. (author), Klinker, F. (author)An analysis is given of possible interference induced by a position marker system, called RASP, into aircraft radio altimeters. The RASP system is used as a marker beacon in flight tests for trajectory measurements, and operates on 4.3 GHz. It is concluded that radio altimeters will not experience any harmful interference from a RASP transmitter.report 1981
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Laan, J.N. (author)It is concluded from this limited analytic study of pure tone sound suppression in a cylindrical duct with uniform flow, based on the mode matching technique, that the optimum of the liner impedance heavily depends on the source distribution and also on the length of the duct.report 1981
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Moek, G. (author)This report constitutes the deposit of a study of literature on martingales and estimation theory. Some experimental work concerning the efficiency of an estimation algorithm based on martingales is also described. The investigation has been guided by the intent to investigate martingales in relation to the Kalman and Kalman-Bucy filters and to...report 1980
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Laan, J.N. (author)A set of equations is presented for the sound propagation in an axisymmetric multisectional duct. For each side of a source section the combined duct effects of transmission, reflection and absorption are reduced to one matrix of coefficients. The procedure is compatible with a source description which takes the feedback of the sound field into...report 1979
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Bosgra, J.A. (author)Noise measurements were performed on two identical space qualified gyroscopes of the floated rate integrating type (Perranti Type I25) in an analog rehalance loop configuration of selectable loop bandwidth, running under space representative conditions. The noise frequency range of interest was O.OO5 Hz to 50 Hz. The noise results were processed...report 1979
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Traas, C.R. (author), Moek, G. (author)The attitude measurement data of the ESA geosynchronous spacecraft METEOSAT have been analyzed using an adaptive recursive filtering technique developed at NLR. The mathematical models of spacecraft dynamics and sensors have been kept very simple. Modelling errors are such that, without adaptive feed-back, strong divergence of the filtering...report 1978
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Wewerinke, P.H. (author)The outside scene is often an important soiirce of information for manual control tasks. In the context of aircraft control the most important example is the visual approach scene. This study deals with modelling the visual scene perception process on the basis of linear perspective geometry and the relative motion cues and investigates its...report 1978
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Hofman, C.F.G.M. (author)Aircraft noise perceived on the ground can be reduced by decelerating the aircraft during the landing approach. As an additional benefit the lower thrust settings existing during a part of the approach and the shorter approach time result in a reduced fuel consumption as compared to a conventional approach. This report deals with an experiment...report 1976
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Laan, J.N. (author)In this report the sound propagation in a hard-walled annular duct of finite length is investigated. The individual modal solutions so found are described. The main properties which are calculated in the present report, are the modal intensity and the modal far field directivity pattern. The modal intensity is determined by the rate of mode...report 1975
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Tiggelaar, J.J. (author)The sound field in an infinitely long duct with shear flow and sound absorbing walls, but with the sound source unspecified, is analysed into its constituents, the acoustic duct modes. The equations, wave numbers, and various properties of the modes are discussed. Some calculated results are used to show the effects of shear flow and absorbing...report 1975
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Ross, R. (author), Rohne, P.B. (author)Measurements of flow disturbances in the NLR - HST on the centerline and at the sidewall showed a maximiun noise level of 1 % in Cprms at a Mach number of 0.8. This is low compared with other ventilated wall tunnels of about the same size. Space-time correlations showed that a large part of the flow disturbances concisted of upstream travelling...report 1973
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Tiggelaar, J.J. (author)For a simplified airplane model in a uniform flow an estimation of the shielding effect of the wing for a single frequency point source of sound is made. The sound field is calculated using a Kirchhoff-type approximation for the boundary values of the field. Some indications concerning the validity of this approximation are mentioned. Results...report 1973