Journal of Energy Engineering

This paper presents an analytical solution that can be used as a simplified design aid when assessing the stability of concrete gravity dams with cracks at their base under usual load conditions. The solution is based on the strength of materials approach. It differs from the classical U.S. Bureau of Reclamation (USBR) gravity method of stress and stability analysis in three ways: (1) The cracks are finite rather than infinite in a direction normal to the dam cross section; (2) the effect of drainage on the stress distribution in the uncracked part of the dam base and at the crack tip is fully taken into account; and (3) the criterion for cracking at the rock concrete interface is based on the effective stress principle used in soil and rock mechanics. The effective stress principle allows the minimum allowable stress at the crack tip to be related to the rock‐concrete interface mechanical properties and the crack drainage properties in a more rigorous manner.

A fully reversible axial flow pump‐turbine is a device that can work as a turbine and as a pump for both forward and reverse directions of flow. These machines find applications in tidal power plants. Double‐cambered S‐shaped profiles are known to be better suited for the blades of such machines; however, information on the aerodynamic characteristics of S‐cambered profiles is very limited. The effect of thickness distribution on the performance of S‐shaped airfoils is considered in this paper. The results obtained from an extensive experimental aerodynamic investigation of three S‐cambered profiles with different thickness distributions are presented. Göttingen 775 and NACA 0010‐66 basic thickness distributions were used to obtain these profiles. The profiles were tested in a wind tunnel in forward and reverse directions of flow. The variation of lift and drag coefficients and that of lift‐to‐drag ratio with angle of attack were obtained. The study showed that among the profiles tested the profile with Göttingen 775 thickness distribution having a maximum thickness at 30% chord is best suited for fully reversible axial pump‐turbine application from the point view of high lift‐to‐drag ratio.

The stability of a controller used to control the water level in the forebay or afterbay of a hydroelectric power plant is investigated by using the Routh‐Hurwitz stability criterion. It is shown how the characteristics of the controller influences the required size of the forebay in a plant with a surge tank, while there are no restrictions regarding stability for a plant without a surge tank. Computer simulations of the water‐level oscillations in a hydropower plant including all major nonlinearities verify these conclusions and show that the operation with small flows is critical as far as the stability is concerned. Guidelines are given to select the dimensions of the forebay for preliminary design. A practical example illustrates the application of this type of control system.

This paper is based on an analysis of turbine cavitation data obtained from 729 turbines installed in the United States since 1950 and 19 selected Canadian turbines. An equation has been developed to express the anticipated rate of cavitation within 75% and 95% confidence limits. The equation is a function of the turbine setting with respect to tailwater, the runner throat velocity, the number of runner blades, the barometric pressure at tailwater less water‐vapor pressure, the runner material, the hours of operation, and the plant‐use factor. The equation can be used to: (1) Select an appropriate setting level for the turbine with respect to tailwater; (2) determine the maximum capacity of a new runner to be installed in an existing casing; and (3) determine the rate of erosion due to cavitation. A preliminary equation also has been developed for estimating the expected efficiency of a new runner in an existing casing, which is a function of the type of casing and draft tube, the number of runner blades, the net head, and the runner throat velocity. Examples of equation use are provided.

A major low‐tech breakthrough in applied thermodynamics employs a new concept for application of combined cycle benefits to increase thermodynamic efficiency of power‐plant turbine cycles. Substantial increases in net plant power output for distribution are readily available. The new low‐temperature engine system (LTES) cycle involves combining a refrigeration cycle and a power turbine cycle. All components involved have a long history of reliability requiring no prolonged new technology research and development program to place a hardware prototype in service. Only the arrangement of these familiar components in combined cycle relationship is new. Thermodynamic relationships between the cycles are reviewed. An analytic method is presented that permits magnitude of potential‐power increases to be expected from LTES for a candidate site to be anticipated without tracing entire cycles. Conventional thermodynamic methods to plan a cycle application are commonplace handbook procedures. Net power‐plant output increases 6% for coal fired plants, 12% for nuclear plants, and 22% for geothermal plants. Environmental benefits are significant.