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Research Papers: Power Engineering

Improved Discharge Measurement Using the Pressure-Time Method in a Hydropower Plant Curved Penstock

[+] Author and Article Information
Adam Adamkowski

Department of Hydraulic Machinery, The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14, PL 80-952 Gdansk, Polandaadam@imp.gda.pl

Zbigniew Krzemianowski, Waldemar Janicki

Department of Hydraulic Machinery, The Szewalski Institute of Fluid-Flow Machinery, Polish Academy of Sciences, Fiszera 14, PL 80-952 Gdansk, Poland

J. Eng. Gas Turbines Power 131(5), 053003 (Jun 09, 2009) (6 pages) doi:10.1115/1.3078794 History: Received September 18, 2008; Revised January 12, 2009; Published June 09, 2009

One of the basic flow rate measurement methods applied in hydropower plants and recommended by the International Standard IEC 60041–1999 and American National Standard ASME PTC 18–2002 is the pressure-time method, generally known as Gibson method. The method consists in determining the flow rate (discharge) by integration of the recorded time course of pressure difference variations between two cross sections of the hydropower plant penstock. The accuracy of measurement depends on numerous factors and, according to the International Standard, generally is confined within the range 1.5–2.3%. Following the classical approach, the pressure-time method applicability is limited to straight cylindrical pipelines with constant diameters. However, the International Standard does not exclude application of this method to more complex geometries, i.e., curved pipeline (with elbows). It is obvious that a curved pipeline causes deformation of the uniform velocity field in pipeline cross sections, which subsequently causes aggravation of the accuracy of the pressure-time method flow rate measurement results. The influence of a curved penstock application on flow rate measurements by means of the considered method is discussed in this paper. The special calculation procedure for the problem solution has been developed. The procedure is based on the FLUENT computational fluid dynamic solver. Computations have been carried out in order to find the so-called equivalent value of the geometric pipe factor F required when using the pressure-time method. An example of application of this method to a complex geometry (two elbows in a penstock) is presented. The systematic uncertainty caused by neglecting the effect of the elbows on velocity field deformation has been estimated.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

A pipeline elbow with marked computational space

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Figure 2

A schematic of the tested turbine flow system

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Figure 3

The velocity magnitude distributions in the penstock cross sections within the elbow no. 2 for mass flow of 200,000 kg/s (Q=∼200 m3/s)

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Figure 4

The values of Δf deviation factor determined for the assumed flow rate values

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Figure 5

Pressure changes measured in the turbine penstock measuring sections and the flow rate determined on this basis

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Figure 6

Turbine efficiency versus mechanical power determined for the F factor calculated directly from the penstock geometry and for the F factor corrected by the developed procedure

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