Frank Kameier

Statistical-Empirical Modelling of Airfoil Noise Subjected to Leading Edge Serrations

With the objective of reducing the broadband noise from the interaction of highly turbulent flow and airfoil leading edge, sinusoidal leading-edge serrations were investigated as an effective passi...

Experimental and numerical investigation of air dam aeroacoustics

Different vehicle manufacturers mount an air dam on the vehicle undercarriage just in front of the wheels. For better understanding of the noise generation mechanisms and flow induced vibrations directly at their source region, the acoustical effects in the interior of the vehicle will be correlated by the University of Applied Sciences Duesseldorf and BMW with the pressure fluctuations of the exterior of the vehicle. Steady state CFD calculations in the area of the rotating front wheel will be carried out for the positioning of the surface microphones and for a better understanding of the flow topology.

Optimised Test Rig for Measurements of Aerodynamic and Aeroacoustic Performance of Leading Edge Serrations in Low-Speed Fan Application

With the aim of analysing the efficiency of leading edge serrations under realistic conditions, an experimental rig was developed where a ducted low-speed fan is installed that allows to gather data of both, aerodynamic and aeroacoustic nature. Turbulent inflow conditions were generated via biplane-square grids, resulting in turbulence intensities of different magnitude and of high isotropic character that were quantified by use of hotwire measurements. The fan blades were designed according to the NACA65(12)-10 profile with interchangeable features and an independently adjustable angle of attack. Altogether, five different parameters can be analysed, namely the serration amplitude and wavelength, the angle of attack, the inflow turbulence and the rotational speed. In addition, the blade design allows for a variation of the blade skew, sweep and dihedral as well. The presented work focusses on validating and optimising the test rig as well as a detailed quantification of the turbulent inflow conditions. Furthermore, first aerodynamic and aeroacoustic results of fan blades with straight leading edges are compared to those of serrated leading edges. The aerodynamic performance was found to be mainly affected by the serrations as a function of the serration amplitude. Aeroacoustically, a clear sensitivity towards different incoming turbulence intensities and serration parameters was detected, showing significant broadband noise reduction below 2 kHz with an overall noise reduction of ΔOASPL = 3.4 dB at maximum serration amplitudes and minimum wavelengths. INTRODUCTION At high-turbulent inflow conditions, the blades of axial fans are known to emit a significantly increased amount of leading edge broadband noise due to the impingement of turbulent structures on the solid surface [1]. Recent research has firmly confirmed leading edge serrations to be an effective passive treatment in both, noise reduction and in increasing specific parameters of the aerodynamic performance such as a delayed stall and high post-stall performance [2–5]. The commonly used scales of importance are depicted in Figure 1, where the peak-totrough value is defined as amplitude A and the distance between two serration roots as the wavelength λ. Up to now, leading edge serrations are mainly analysed in wind tunnel experiments where rigidly mounted aerofoils are tested. In preliminary studies Biedermann et al. analysed a NACA65(12)-10 aerofoil with and without sinusoidal leading edge serrations both, aeroacoustically and aerodynamically by use of experimental and numerical approaches [2,6,7]. A statistical-empirical model was developed to predict the broadband noise emissions by taking into account the chord based Reynolds number, the incoming turbulence intensity, the angle of attack as well as the serration parameters amplitude and wavelength. A clear ranking of the main influencing factors could be shown and, moreover, significant interdependencies between the influencing parameters could be detected as well. As Figure 2 shows, the Reynolds number (Re) and the freestream turbulence intensity (Tu) are identified to be the main contributors to the broadband noise emissions. With the Proceedings of ASME Turbo Expo 2018 Turbomachinery Technical Conference and Exposition GT2018 June 11-15, 2018, Oslo, Norway

DEAP-based energy harvesting using vortex-induced vibrations

Generators based on dielectric electroactive polymers (DEAP) convert mechanical strain energy into electrical field energy. In order to harvest renewable energy from ambient sources adequate generator setups have to be developed. Thus, in this contribution a DEAP generator is presented which uses periodic vortex induced vibration of a circular cylinder as excitation mechanism, by which e.g. Flow energy of a wind or water current can be converted. For this purpose a novel generator design consisting of a cylinder that is elastically mounted on DEAP material is presented. Since the effect of vortex induced vibrations depends on the stiffness and damping of the utilized generators eigenmode, a method to adapt both via the electrostatic pressure and energy conversion is proposed. After the validation of the general functionality of the novel generator design, analyses concerning the control of the overall harvester are carried out.

Enforcement of Flow-Induced Oscillations of a Circular Cylinder due to Interference Effects -Numerical Simulations and Experimental Studies-

The enforcement of flow induced oscillations of a spring mounted circular cylinder (dcyl) due to the presence of a fixed square cylinder (ds.cyl) is investigated. An integrated approach takes place by means of 2D CFD simulations and experimental studies in the wind tunnel. The results show that a reduction of the square cylinder distance (g) leads to a higher oscillation of the upstream cylinder (until a critical distance is reached). Furthermore, there is an enlargement of the flow velocity region where lock-in takes place (factor 4 at g/dcyl = 0.8). The main reason for those phenomena that can be found is the raising pressure field downstream of the cylinder due to the square cylinder interference. This increased pressure field leads to a reduction of the separation angle which controls the lift force of the upstream cylinder. The alternating vortices are now farther away from one another what increases the time of their energy absorption before they cut each other off. The reduced vortex interaction leads to a slower rise of the phase angle between lift force and cylinder movement with increasing flow velocity. Hence the vortex separation pattern remains longer in the 2S mode where higher lift forces occur than in the self-limiting 2P mode. Therefore the leaving of the lock-in region at a critical phase angle can be delayed.

Experimentelle und numerische Untersuchung zur Strömungsakustik einer Staulippe

Die Staulippe befindet sich an Fahrzeugen unterschiedlicher Automobilhersteller am Unterboden jeweils vor den Radern. Ihre akustische Wirkung im Fahrzeuginnenraum wird im Rahmen einer Untersuchung der FH Dusseldorf und BMW mit Druckschwankungen an der Fahrzeugau:sBenseite korreliert, um den Ent stehungsmechanismus von Gerauschen und stromungsinduzierter Schwingungen bereits im Quellbereich besser zu verstehen. Fur die Positionie rung der Wandmikrofone und fur ein tieferes Verstandnis der Stromungstopografie werden stationare CFD-Rechnungen im Bereich des rotierenden Vorderrades durchgefuhrt.