Investigation of cavitation damage to baffle piers and flow splitters

Abstract

In hydraulic engineering, wide use is made of baffle piers and flow splirtem (including spreaders), whichspread and dissipate excess flow energy, and reduce the scour downstream. However, with velocities greater than 12-15 m/sec, cavitation and cavitation damage of the energy-dissipating elements may occur. Serious cavitation damage of energy dissipators and stilling basin elements has occurred at Bonneville dam (usA), the V. I. Volga hydroelectric plant, the Novosibirsk hydroelectric plant, the Norfolk dam (USA), and others [1].The problem of cavitaticm damage prediction to the different elements of spillway structures has not been sufficiently studied; for this reason, attempts made up to the ixesent time to prevent cavitation (including baffle piers and flow splitters) have not been always successful, especially for velocities greater than 25 m/sec ~2, 3, 4, 10]. However, it is pc~ible to develop baffle piers which, because of their shapes, may operate under cavitation conditions without undergoing any cavitation damage. This development is highly promising, since with its success, the field Of application of baffle piers and flow splitters would be considerably expanded. In order to prevent cavitation damage to these suuctures, it is necessary to design them on the basis of a thorough knowledge of their detailed cavitation characteristics. Sufficiently reliable values of these characteristics were obtained from model tests in large high-vacuum cavitation installations in which the corresponding hydraulic conditions were relxoduced . including the hydraulic jump, taking into consideration that the structure and pulsation characteristics of the flow effect the process of inception and development of cavitation and cavitation damage, which made it nece~ary to adhere to Froude's similitude conditions.* To have approximate similitude in the cavitation phenomenon, it is necessary to fulfill the condition Kprot = ~Kmod (1) in which Kprot and KmO d are the cavitation parameters for the prototype and model; 71o = f(Remod, We) is the correction coefficient for the scale of the model (it was a~umed that 77o = 1, taking into consideration the large scale of the model, Re -~ 10s-10s). Absence of cavitation is ensured under the conditionKprot >leer (2) in which Ker is the critical cavitation parameter, that is, the parameter for the inception of cavitation. The ratio K/Ker characterizes the stage (or degrhe) of the development of cavitation.The cavitation parameter is usually expressed in the form K : Hchar --Herin which Hchar = H a + h, H a is the head at the free surface of the flow, in meters; for the prototype, H a is the atmospheric pressure; h is the height of the water column above the energy disaipatcr m; Her is the critical vapor pressure, in meters of water; Hcr = Pd/7; Pd is the vapor pressure, in meters of water; and Vchar is the characteristic velocity of approach (taken from the velocity distribution diagram), m/sec.In order to produce cavitation damage in the high-vacuum installation at velocities of 5-10 m/...

Hydrodynamic characteristics of water flow in area of lower pool junction of spillway structures

“…In general, in hydraulic complex spillway structure calculation of the impact plates' length and thickness, the energy extinguishers' location and the hydrodynamic stresses on them, the mode of flow movement in the apron and risberme, and the magnitude of the local flushing behind the structure. N.P.Rozanov [2,3], a scientist who conducted experimental studies to determine the hydrodynamic characteristics of the lower pool of hydraulic structures, argued that it is advisable to build devices such as water tanks, wall rows, and platforms in the area of the first hydraulic jump behind the compressed section after the power switches.…”

Effect of flow velocity on downstream energy absorbers and velocity coefficient

“…The reaction of absorbers and expressions of their dependence on their shape, geometric dimensions, and location can only be obtained by conducting experimental studies. In this case, the most difficult task is determining the flow velocities impacting the absorbers and their resistance coefficients [10][11][12][13][14][15][16].…”