This experimental study was carried out at a free-stream Mach number of 0.6 and a Reynolds number per foot of 3.45 x 106. The magnitudes of the wall-pressure fluctuations agree with the Lilley-Hodgson theoretical results. Space-time correlations of the wall-pressure fluctuations generally agree with Willmarth's results for longitudinal separation distances. The convection velocity of the fluctuations is found to increase with increasing separation distances, and its significance is explained. Measurements with the longitudinal component of the velocity fluctuations indicate that the contributions to the wall-pressure fluctuations are from two regions, an inner region near the wall and an outer region linked with the intermittency.

Surface pressure fluctuations below turbulent boundary layers were studied, in part, because they can be regarded as 'footprints' of passing turbulent eddies. The pressure fluctuations are formally described by a Poisson equation, implying that the pressure fluctuation at a given point is mathematically represented by the integral of a 'source' term over the whole flow field, with a weighting inversely proportional to the distance of the source from the given point. In turbulent boundary layers, fluctuations were made in a low-speed constant pressure the high-frequency part of the wall pressure fluctuations is generated mainly within the inner layer - say, the first 20% of the boundary layer thickness - and the low-frequency part is generated mainly in the outer layer. Measurements of velocity and surface-pressure turbulent boundary layer well downstream of an extensive region of wall roughness. The turbulence near the wall was representative of a smooth-wall flow, while that in the outer layer was typical of the upper stream rough-wall flow. Comparison with previous measurements on an entirely smooth wall illustrates the relative contributions of the inner and outer layers to the surface pressure fluctuations. Further work has been done to compare the VITA (Variable ge) conditional-sampling algorithm withuctuations were more advanced algorithms. Keywords: Turbulent boundary layer, Noise measurement, Statistical analysis, Surface roughness, and VITA algorithm.

Smol'yakov and Tkachenko's book is a very thorough and detailed survey of the response of hot wires and related trans ducers to a fluctuating flow field. Now that the electronic equipment needed for hot-wire anemometry is so easy to make or cheap to buy, transducer response is the most critical part of the subject - except for the fragility of the sensing element , for which textbooks are no remedy! We hope that this book will be useful to all students and research workers concerned with the theory or practice of these devices or the interpretation of results. Peter Bradshaw Imperial College London v Preface "The importance of experimental data and of experimentally established general properties is often underestimated in the study of turbulence . . . •. The most direct path is to use experimentally established properties as the foundation upon which models explaining these properties can be constructed. " M. D. Millionshchikov Turbulence belongs to a class of physical phenomena that are very frequently encountered in both nature and technology. It is the most common and also the most complicated form of motion of real liquids and gases. It is observed in the oceans, in the atmosphere, and in a very wide range of systems in engineering. The rational design of airplanes, rockets, ships, dams, hydroelectric plant, canals, turbines, ventilators, and many other technological systems must involve the consideration of turbulence.