Instrumentation requirements for laminar flow research in the NLR high speed wind tunnel HST

It is noted that the testing of laminar flow airfoils and wings in wind tunnels imposes very stringent requirements on the wind tunnel and the measurement techniques. Starting from experience obtained in the high-speed tunnel (HST) of the NLR, typical aspects such as scale effects, flow quality, and model contamination are discussed. Different techniques of transition detection are reviewed, and it is concluded that the infrared technique in combination with continuous wake rake traverses provides the best opportunity for a detailed experimental analysis of a particular laminar flow design. Drag measurements by means of continuous wake rake traverses with electronically scanned pressure transducers provide the required detail for drag evaluation. The NLR HST fulfils these requirements for laminar flow testing in a cost-effective way