v58-65 - good information obtain from intenet

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Abstract —Preliminary results for a new flat plate test facility are presented here in the form of Computational Fluid Dynamics (CFD), flow visualisation, pressure measurements and thermal anemometry. The results from the CFD and flow visualisation show the effectiveness of the plate design, with the trailing edge flap anchoring the stagnation point on the working surface and reducing the extent of the leading edge separation. The flow visualization technique demonstrates the two-dimensionality of the flow in the location where the thermal anemometry measurements are obtained. Measurements of the boundary layer mean velocity profiles compare favourably with the Blasius solution, thereby allowing for comparison of future measurements with the wealth of data available on zero pressure gradient Blasius flows. Results for the skin friction, boundary layer thickness, frictional velocity and wall shear stress are shown to agree well with the Blasius theory, with a maximum experimental deviation from theory of 5%. Two turbulence generating grids have been designed and characterized and it is shown that the turbulence decay downstream of both grids agrees with established correlations. It is also demonstrated that there is little dependence of turbulence on the freestream velocity. Keywords CFD, Flow Visualisation, Thermal Anemometry, Turbulence Grids. I. INTRODUCTION HE ability to predict transition is becoming an ever more important requirement in many areas of engineering and plays an essential role in many aerodynamic applications where the desire to employ large regions of laminar flow is advantageous. The development of theoretical methods for transition prediction depends on sufficiently detailed experimental data to describe the complex physical processes involved. The effect of freestream turbulence (FST) on the onset of transition has received great attention in the last number of years [1]-[5], and is of great interest, for example, in the area of turbine blade design, where the impingement of turbulence from the wake of the stator influences the boundary layers on the rotor blades [6]. It is widely known that an elevated FST level causes transition to occur more rapidly. Reference [7] introduced the term ‘bypass’ transition and this N. Patten is with the Mechanical and Aeronautical Engineering Department, University of Limerick, Ireland (353-61-213134; e-mail: [email protected]). T. M. Young is with the Mechanical and Aeronautical Engineering Department, University of Limerick, Ireland. P. Griffin is with the Mechanical and Aeronautical Engineering Department, University of Limerick, Ireland. type of transition can occur in the presence of large, nonlinear disturbances (e.g. elevated FST, usually above 1% of the freestream velocity). Amplitude and spectral characteristics of the disturbance strongly influence which type of transition occurs. Transient growth occurs when two nonorthogonal, stable modes interact and grow [8]. The path to transition for
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v58-65 - good information obtain from intenet

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