9574065333

Krzysztof Olasek, Maciej Karczewski

a modernised wind tunnel test stand adapted for the aerodynamic experiment with the use of Particie Image Velocimetry (PIV) measurement system (1). This is a modern, high-efficiency tool for laser-based velocity flow measurements. For the flow velocity measurements, the PIV technique has few advantages over traditional methods, such as pressure probe-based methods. The most important ones are:

-    PIV provides an instantaneous information about the flow velocity in a large measurement area (in opposition to very local measurements possible with pressure probes, Constant Temperaturę Anemometry (CTA) or Laser Doppler Anemometry (LDA) techniques),

-    obtained velocity field has at least a satisfactory spatial resolution (in the order of magnitude of millimetres - such a resolution can be obtained only with very dense traversing of standard measuring equipment),

-    measurement process is non-invasive (there is no need to introduce any object into the flow as in the case of pressure probe measurements or hot wire anemometry).

Obtaining an instantaneous, broad velocity field, besides providing obvious information about the measured flow characteristics, opens up several other potential applications of PIV-gathered data as described in this paper. The character of PIN/ results makes it a perfect experimental method for verification of simulation results obtained by means of Computational Fluid Dynamics (CFD). Numerical results can be easily validated by aerodynamic experiment thanks to relatively easy comparison of velocity fields obtained by the two methods. For example, subtraction of the computed and measured flow fields gives immediate information about differences and can aid in establishing concrete level of confidence ratio for the numerical model, even at the very local level. On the contrary, in the classical approach, often, the validation of a numerical model is done only by qualitative analysis of the velocity field and measured flow structures. Having the PIN/ results, however, an experimenter can perform morę advanced quantitative analysis as well. The suggested method allows to extract additional information from the velocity field providing data about the dynamics of the flow as well.

This paper presents preliminary results of lift coefficient calculations basing on velocity fields obtained from the CFD simulation of the quasi-3D flow around NACA0012 airfoil. Before applying it to the wind tunnel experimental data, a decision was madę to test the algorithm on CFD results. CFD is a reliable reference data because it provides a complex and undisturbed velocity field data (in opposition to every experiment) and allows to obtain the aerodynamic loads on analysed airfoil directly by force exerted on the walls of the numerical model.