Seeding technique for Laser Doppler Velocimetry measurements in strongly accelerated nozzle flowfields

Development of a solid particle seeding technique to eliminate particle lag biasing of Laser Doppler Velocimeter (LDV) data encountered in two shock-free, transonic flow experiments is described. Biasing, caused by seed particle agglomeration, can result in mean velocity measurement errors in excess of ten percent and errors in turbulence parameters an order of magnitude larger. The new system, which made use of particle separators in conjunction with changes in the optical arrangement and seed handling procedures, is shown to reduce mean velocity lag bias to less than one percent. Based on this study, recommendations are presented regarding the diagnosis of a potential or existing particle lag bias problem and means to reduce such bias in LDV experiments.