State-of-the-art and future prospects of non-intrusive measurement techniques for aerodynamic design

Kurzfassung

During the last decade several advanced non-intrusive measurement techniques such as microphone arrays for sound source location, pressure sensitive paint (PSP) for pressure measurements on the complete surface of a model in the wind tunnel, laser Doppler velocimetry (LDV), particle image velocimetry (PIV), and Doppler global velocimetry (DGV) for large field and instantaneous velocity measurements have been developed. Due to the fast progress made in the field of computers, lasers, electronics, video technique etc. it was possible to set up reliable, modular and mobile advanced measurement systems for use in industrial test facilities such as large wind tunnels. After a brief characterization of the different techniques the qualitative and quantitative improvements achieved during the past few years will be demonstrated taking the PIV technique as an example. PIV allows the recording of a complete velocity field in a plane of the flow within a few microseconds. Thus, PIV provides information about unsteady flow fields, which is difficult to obtain with standard non-optical and intrusive experimental techniques. The short acquisition time and fast availability of data obtained by the advanced experimental techniques reduce the operational time, and hence cost, in large scale test facilities. The quality of the data obtained in complex unsteady flow fields by means of these techniques allows detailed comparison with the results of numerical calculations. It is expected that this fast and immediate comparison will change the way wind tunnel tests will be organized in the future from a top-down approach with a given test plan to a rather interactive procedure. This, however, will require the development of tools for fast alignment and calibration of the experimental set up and on-line evaluation, for comprehensive postprocessing and data reduction tools in order to compare and analyze experimental and numerical data during the test, and for easily understandable presentation of the results to the end user. Moreover, advanced measurement techniques for measurement of pressure, velocity, density and model deformation must be further developed in order to be able to employ them in parallel (especially in unsteady flows) to provide the complete information about the flow field.