Lift fluctuations on aerofoils in transverse and steamwise gusts.
A program of research is described which investigated the aerodynamic reponse of an isolated aerofoil to an unsteady field of flow, The effects df both 'transverse gusts' as considered by Karman and Sears (13) and 1 streamwise gusts' as considered by Horlock (4 0), have been studied. To enable actual lift and pressure fluctuations to be measured a gust tunnel capable of producting both types of gust has been designed and built. The lift response to a transverse gust was found to compare well with Kemps (49) theory although the pressure distribution was not as expected. This result and those obtained with the streamwise gust suggest that the behaviour of the wake and the exist~nce of a separation region seriously affects the validity of the classical vortex based solutions. The compatibility between Hor lock 1 s analysis and the analysis of Sears (47) h~s been demonstrated. The author has also supplemented the existing theories to provi~e -a basic set of thin aerofoil response functions. These functions are -presented and tabulated. - Design criteria for the . minimisation of the fluctuating lift are suggested for both the compressor and the turbine flow. In a further theoretical investigation the importance of the correct r epresentation of the wake is demonstrated. The effect of a failure to allow for it at all and the effect of misrepresenting its speed of propagation are both analysed. A survey of the literature covers the American, German and Russian schools with their distinctly different approaches. In particular an attempt � has been made to identify those theories which have a greater range of validity than the basic theory.
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