ON THE OVERESTIMATION OF THE FLOW TURBULENCE DUE TO FRINGE DISTORTIONIN LDA MEASUREMENT VOLUMES

Fringe distortion with linear longitudinal variation in fringe spacing over the length of LDA measurement volume has been considered to infl uence the accuracy of flow measurement. The overestimation of the mean velocity and especially of the flow turbulence due to fringe distorti on has been derived to be a function both of the fringe distortion num ber (which is a purely geometrical parameter of the measurement volume ) and the flow turbulence to be measured. Against the usual expectatio n, it has been shown that the overestimation of the flow turbulence du e to fringe distortion in the measurement volume could be neglected. O nly for very low turbulence intensity dose the error become significan t. As a reference this result could be used to estimate measurement er rors which occur in the presence of other types of fringe distortion.