Effects of non-homogeneous flow on ADCP data processing in a hydroturbine forebay

Abstract

Accurate modeling of the velocity field in the forebay of a hydroelectric power station is important for both power generation and fish passage, and is able to be increasingly well represented by computational fluid dynamics (CFD) simulations. Acoustic Doppler Current Profiler (ADCP) are investigated herein as a method of validating the numerical flow solutions, particularly in observed and calculated regions of non-homogeneous flow velocity. By using a numerical model of an ADCP operating in a velocity field calculated using CFD, the errors due to the spatial variation of the flow velocity are quantified. The numerical model of the ADCP is referred to herein as a Virtual ADCP (VADCP).Two applications of the VADCP are modeled in the numerical analyses presented. Firstly the virtual measurement error of the VADCP is calculated for a single instrument adjacent to the short converging intake of a powerhouse. Secondly, the flow discharge through the forebay is estimated from a transect of VADCP instruments at different distances from the powerhouse. The influence of instrument location and orientation are investigated for both cases.A velocity error of up to 94% of the reference velocity is calculated for a VADCP modeled adjacent to an operating intake and is shown to decrease with distance from the powerhouse. Qualitative agreement is observed between the calculated VADCP velocities and reference velocities by a horizontal offset distance of 18m upstream of the powerhouse.