Principles and Measuring Techniques of Turbulence Characteristics in Open-Channel Flows
open channel flow, streams, turbulence
Journal or Book Title
Geological Survey Professional Papers
Turbulence velocity fluctuations in open-channel shear flows cause or strongly influence a large number of fluid-mechanics phenomena of interest to engineers. Turbulence measurements in fluids have been made with varying degrees of success, but only recently have measurements of turbulence in water been made with any degree of reliability. This recent improvement is due to the development of hot-film anemometry, which has given the researcher a tool for studying the structure of turbulence in open-channel flows. The fine spatial resolution (due to the small size of the sensor) and the good frequency response of the hot-film anemometer system are unmatched by any other system now available for making turbulence measurements in open-channel flows. This report describes the statistical turbulence characteristics that best define the structure of the flow field and the relation between the characteristics and the equations of motion and energy. A detailed description of instrumentation, sensor selection, and theory of operation is presented along with a discussion of calibration characteristics, heat-transfer relations, hot-film and hot-wire measurements, and possible sources of errors in turbulence measurements. The report explains in detail a procedure to circumvent contamination problems so that measurements can be made in natural rivers and streams; it also presents a mathematical and experimental justification for the procedure. Aspects of analog and digital data reduction are discussed along with some guidelines to insure meaningful measurement of turbulence characteristics.