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Title: Pressure fluctuations in the plunge pool of an impinging jet spillway
Author: Withers, William James
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1991
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The primary purpose of this dissertation is to define the range of pressure fluctuations produced at a plunge pool floor due to spillway jet impingement. At high head dams the spillway flow sometimes takes the form of free- falling jets. Energy dissipation of the spillway flow is achieved by dispersion of the free-falling jets in the atmosphere, diffusion of the impinging flow in a water cushion at the dam base and impact of the remaining flow with the plunge pool floor. The plunge pool may be formed naturally through scouring of the bedrock by the spillway flow or may consist of a man- made stilling basin. Whichever method is adopted, impingement of the spillway jets with the plunge pool tailwater promotes a large degree of air entrainment while mixing of the pool fluid with the incoming flow generates a large amount of turbulence. Associated with the turbulence are large pressure fluctuations which act on the sides and floor of the stilling basin. In the case of lined pools, the fluctuations can cause uplift and removal of the concrete base slabs from the stilling basin. Damage of this form may become severe and, if left unchecked, produce subsequent failure of the dam. Vibration of the dam due to coincidence of the structures natural frequency with that of the applied loading is also a threat. In natural plunge pools, excessive scour can be produced, possibly undermining the dam foundations. In general, lack of information has meant that current stilling basin design procedures usually fail to include these pressure fluctuations in the structural design of the plunge pool. The objective of this research is to establish information describing pressure fluctuations for design use and prevent these forms of operational problems. The highly complex flow situation was simulated. by construction of an experimental rig at the University of Glasgow. Design of the apparatus was such that the main parameters affecting the flow could be altered to cover a wide range of scenarios. As well as measurement of instantaneous pressures on the plunge pool floor, turbulence readings within the plunging jet were taken as the behaviour of the free- falling flow has a profound effect on the subsequent plunge pool diffusion. The current state of technology allowed data acquisition and control by means of a micro- computer. By development of analytical procedures and specialised routines from commercial software, the computer was used to facilitate measurement of pressure fluctuations at selected locations on the plunge pool floor and velocity fluctuations within the plunging jet. The raw data was then statistically analysed with the primary interest being the magnitude, frequency and extent of pressure fluctuations at the pool base and the turbulence development within the plunging jet. From the jet turbulence results, methods were produced to determine the jet condition at impact with the pool surface for comparison with measured values. The statistical pressure head results were compared with other available research and parameters were introduced to take account of the effects of plunging jet behaviour in the atmosphere on the subsequent plunge pool diffusion process. Through analysis, explanation of the values of mean pressure head and the level of fluctuations generated at the pool floor was provided. Application of the results to plunge pool design was also included.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)