An experimental study was conducted to measure the growth rates of mechanically generated surface water waves when subjected to a fully developed turbulent channel airflow. The study was designed to test the accuracy of the growth rates predicted by Miles's (1962b) theory. For a series of wave frequencies (from 2·04 to 6·04 Hz at 0·50 Hz increments) and centre-line wind velocities (0·20, 1·12 and 1·84 m/s) wave amplitudes were measured at three stations (2–21, 3–43 and 4·65 m) downwind from a wave generator. In addition, for centre-line velocities of 1–12 and 1·84 m/s, U* (the velocity at the outer edge of the viscous sublayer) and U1, (the shear velocity) were obtained from measured mean velocity and Reynolds stress profiles. The wave amplitude measurements at the wind velocity of 0·20 m/s provided attenuation rate estimates which agreed reasonably well with theoretical attenuation rates based on viscous effects both on the walls and in the bulk of the water. The amplitude measurements at the wind velocities of 1·12 and 1·84m/s provided growth rate estimates which were compared with theoretical growth rates (computed using the wave frequency, U1 and U* predicted by Miles's (1962b) theory. At 1·12m/s Miles's growth rateswere two to five times larger than those measured; at 1·84 m/s Miles's growth rates were about two times larger.
AB)TRACTIn studies of wave generation an exploration of the wind field close to the water surface is critical.Such an exploration can be made with a hot-wire or film anemometer mounted on a device driven by a servomechanism which will maintain the anemometer at a fixed distance from the fluctuating water surface. This report describes the CBI Wave Follower which has been designed to hold anemometers at fixed distances from 60 cm to I cm from the water surface. It may be used with waves up to 30 cm in height. It allows adjustment for tidal changes in mean water elevation up to 60 cm and for slow vertical scanning. J ACKNOWLEDGEMENTSTo bring the wave follower into existence has required knowledge and know-how of many different kinds. Over the two years that it has been building the authors have sought help when and where they could find it. For this reason, it has become impossible to properly acknowledge and, in some cases, even identify individual contributionE.The authors are no less grateful to those who have helped and whose names do not appear here than they are to those specifically mentioned.General guidance during the development of the wave follower and assistance in preparing this report were given by Dr. B. Kinsman.The machining of parts which were often complex and subject to irritating modifications was cheerfu2ly and skillfully done by Messrs. S.Krausman, M. Fischer, B. Baker, and R. Faulkner. Mr. E. Schiemer designed the mounting pedestal. We have drawn heavily on the skill and knowledge about hot-wire anemometry of Messrs. F. Merceret, Jr.and M. Banner.
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