Acoustic discharge measurements for the performance testing of low-head hydroelectric turbines under disturbed flow conditions

Abstract

Field performance testing of a low-head hydroelectric turbine is essential to evaluate the efficiency and economics of an operation. For low-head hydroelectric turbines, it is difficult to accurately measure the discharge through a unit. Transit-time velocity measurement technology has recently been used to develop, in a laboratory setting, a unique traversing acoustic discharge meter for low-head hydroelectric applications. This technology was recently combined with Gauss-Legendre quadrature integration as an alternative method of measuring the flow through a low-head hydroelectric turbine. However, laboratory testing of this technology has only dealt with undisturbed or ideal flow conditions. Additional physical modeling has been performed to compare the relative accuracy of the continuous traversing acoustic discharge meter with that of a multilevel Gauss-Legendre quadrature integration in disturbed or nonideal flow conditions. The data indicate that while Gauss-Legendre quadrature may provide more accurate estimates in ideal flow conditions, the continuous traversing acoustic discharge meter is better suited to disturbed flow condition because it can better resolve an intricate velocity profile. The accuracy of this instrumentation is sensitive to relatively large scale vorticity rotating in the plane of the acoustic transducers, although accuracies within 2% are still attainable, which is better than the conventional velocity-area method. Key words: acoustic discharge measurement, disturbed flow, turbine, performance testing.