This paper describes an extensive assessment and a step by step validation of different turbulent boundary‐layer trailing‐edge noise prediction schemes developed within the European Union funded wind energy project UpWind. To validate prediction models, measurements of turbulent boundary‐layer properties such as two‐point turbulent velocity correlations, the spectra of the associated wall pressure fluctuations and the emitted trailing‐edge far‐field noise were performed in the laminar wind tunnel of the Institute of Aerodynamics and Gas Dynamics, University of Stuttgart. The measurements were carried out for a NACA 643‐418 airfoil, at Re  =  2.5 ×106, angle of attack of −6° to 6°. Numerical results of different prediction schemes are extensively validated and discussed elaborately. The investigations on the TNO‐Blake noise prediction model show that the numerical wall pressure fluctuation and far‐field radiated noise models capture well the measured peak amplitude level as well as the peak position if the turbulence noise source parameters are estimated properly including turbulence anisotropy effects. Large eddy simulation based computational aeroacoustic computations show good agreements with measurements in the frequency region higher than 1 kHz, whereas they over‐predict the sound pressure level in the low‐frequency region. Copyright © 2011 John Wiley & Sons, Ltd.

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A semi-empirical model to determine the wall pressure frequency spectrum beneath a twodimensional, pressure gradient turbulent boundary-layer is presented. The model is derived based on the experimental wall pressure data of various research groups. The experimental database includes both the equilibrium flat plate and non-equilibrium airfoil boundary-layer flow cases and covers a large range of Reynolds numbers, 1.0 × 10 3 < Re δ 2 < 3.0 × 10 4. The enhanced model is a combination of the modified Chase-Howe, Goody and Rozenberg models, and is a simple function of the ratio of pressure and timescales of the outer to inner part of the boundary-layer. The key advantage of the present model is that it incorporates the Reynolds number, the boundary-layer loading as well as pressure gradient effects through an amplitude scaling function and timescale ratio, and compares well to the experimental data. Spectral features of the detailed measurement data and various scaling behavior of the wall pressure spectrum are elaborately investigated. A summary of the results on the applicability and limitation of the model for various test cases is discussed. The enhanced model is further applied to develop an airfoil turbulent boundary-layer trailing-edge interaction (TBL-TE) far-field noise prediction scheme. Prediction results are compared with the well established experimental database and encouraging results are found. The enhanced Wall Pressure Fluctuation (WPF) as well as trailing-edge noise spectra models accuracy for the maximum noise level is in ±2dB range for the test cases examined. The model can be applied further for acoustic airfoil design and optimization and in various aeroacoustic applications. NOMENCLATURE Latin & Greek Symbols c [m] Chord length C f [−] Skin friction coefficient, C f = τ w /0.5ρ ∞ U ∞ 2 c 0 [m/s] Speed of sound

A tool for the numerical shape optimization of axisymmetric bodies submerged in incompressible flow at zero incidence has been developed. Contrary to the usual approach, the geometry of the body is not optimized in a direct way with this method. Instead, a source distribution on the body axis was chosen to model the body contour and the corresponding inviscid flowfield, with the source strengths being used as design variables for the optimization process. Boundarylayer calculation is performed by means of a proved integral method for attached laminar or turbulent boundary layers. To determine the transition location, a semi-empirical method based on linear stability theory (e n-method) was implemented recently. A commercially available optimizer as well as an evolution strategy with covariance matrix adaption of the mutation distribution are applied as optimization algorithms. Shape optimizations of airship hulls were performed with this new tool for different Reynolds number regimes. The objective was to minimize the drag for a given volume of the envelope and a prescribed airspeed range. The results obtained show a high sensitivity of the optimization result towards the transition criterion used. Nomenclature A amplitude of a Tollmien-Schlichting wave c d drag coefficient c d V volumetric drag coefficient D drag f frequency H12 shape factor n amplification factor N total number of source sections q0 i source strength at the beginning of the i th section q1 i source strength at the end of the i th section r0 i distance from start of i th source section to field point r1 i distance from end of i th source section to field point Re Reynolds number