A Survey of the Utilitarian Aspects of Advanced Flowfield Diagnostic Techniques

A in electronics, material technology, and computers have made it possible to improve wind tunnel instrumentation at a rate commensurate with increasingly stringent demands for greater instrumentation accuracy and versatility in complex flowfields. As a result, the opportunity exists today to use diagnostic techniques that were not available a decade ago. It is necessary to learn enough about the strengths and weaknesses of each new technique to determine how and when to use it to good advantage. The literature contains ample information on the basic principles of operation, but many reports extol the virtues of the technique without discussing its limitations. Furthermore, there is a conspicuous absence of utilitarian information on cost, development time, and other considerations which may be important factors in deciding whether the technique should be applied to a specific flowfield measurement problem. In order to obtain practical information on diagnostic techniques, a questionnaire was sent to all members of the Supersonic Tunnel Association (STA) requesting detailed responses to questions on technique capabilities, cost, source, supporting instrumentation, calibration procedures, data reduction requirements, development time, and manpower needs. Nineteen STA organizations from seven different countries returned more than sixty questionnaires which are summarized in this paper. Based on the returned questionnaires, the respondents have designated as advanced any diagnostic techniques incorporating nonintrusive (optical) measurements or requiring high data rates. The optical techniques surveyed in this paper include Raman and Rayleigh scattering, holography, interferometry, the electron beam, and laser velocimetry. In addition, completed questionnaires were received on timeresolved measurements from probes inserted into the flow, such as the hot-wire and rapid-response pressure probes. This survey paper cites basic references and reviews the operation, measurement capabilities, and utilitarian aspects of each of these flowfield diagnostic techniques.