Current Meter Method Research Articles

Research of Turbine Efficiency Test by Current-Meter Method in Circular Pipe

For absolute discharge and efficiency measurement of turbine with medium and low water head, the current-meter method has high precision, good reliability, and wide application range. For rectangle flow channel, it is easy to lift down a gate frame with current meters to measure the flow velocity, but for circular pipe, due to the high stress, possible deformation, and strict safety requirement, the design, installation, and implementation of the support bracket is the key to the measurement by current-meter method. In this paper, we made the research of key technology for current-meter method in circular pipe. By building a numerical model for circular pressure pipe and flow measuring bracket, we analysed the influence of meters arrangement, the force and deformation of support pole with CFD, and fluid-solid coupling method, Finally, an optimized reinforcement bracket is proposed, with combined smooth and stress calculation, the measuring bracket is verified it can withstand the flow stress and has good safety characteristics, which can provide a reference for other similar turbine efficiency tests.

Calibration of Winter-Kennedy coefficients on a Bulb turbine based on current-meter method

Field measurement of discharge has been performed for a Bulb turbine based on current-method in this paper. Winter-Kennedy coefficients of this machine are calibrated based on the test results of integrated discharge and measured flow differential pressure between bulb head and stay cone. Calibration shows that discharge and flow differential pressure of the test machine follow the power model very well. The uncertainty of discharge estimation by Winter-Kennedy method for Bulb turbine is discussed finally.

Field test for hydraulic turbine discharge and efficiency based on current-meter method

Hydraulic turbine efficiency is one of the important indicators during acceptance inspection. One of the difficulties in field test for hydraulic turbine efficiency is discharge measurement. Current-meter method is widely applied because of its intuition and accuracy. Through test in a Francis turbine with a circular penstock, turbine discharge and efficiency calculation based on current-meter method is discussed in this paper. Test results indicate that integration step-size needs to be small enough to get accurate discharge in graphical integration method. Uncertainty estimation is important and requisite in field test for turbine efficiency, which reflects the actual reliability of test results.

The comparative analysis of the current-meter method and the pressure-time method used for discharge measurements in the Kaplan turbine penstocks

The paper presents experiences gathered during many years of utilizing the current-meter and pressure-time methods for flow rate measurements in many hydropower plants. The integration techniques used in these both methods are different from the recommendations contained in the relevant international standards, mainly from the graphical and arithmetical ones. The results of the comparative analysis of both methods applied at the same time during the hydraulic performance tests of two Kaplan turbines in one of the Polish hydropower plant are presented in the final part of the paper. In the case of the pressure-time method application, the concrete penstocks of the tested turbines required installing a special measuring instrumentation inside the penstock. The comparison has shown a satisfactory agreement between the results of discharge measurements executed using the both considered methods. Maximum differences between the discharge values have not exceeded 1.0 % and the average differences have not been greater than 0.5 %.

A Simple and Inexpensive Method for Determining Stream Discharge from a Streambank

ABSTRACT A detailed protocol for the determination of stream discharge is presented which requires neither a current meter nor actual entry into streamwater. The protocol represents a modification of the flotation method of discharge determination and was devised in response to the need for a simple, inexpensive, “bank-side” technique for estimation of stream flow. Discharge is determined through measurements of a stream's cross-sectional area and surface velocity. In tests at high and low flows, mean discharges determined by the proposed flotation method were not significantly different from those calculated using a standardized, current-meter method. This suggested that me proposed flotation method (a 10–20 min procedure) could be used with reasonable accuracy to determine discharge in small to moderate-sized streams.

Water Gaging for Low-Head Units of High Capacity

Abstract In the field of hydroelectric construction there has been in recent years considerable advance in the development of low-head units of high specific speed. This tendency in design has been conducive to the development of low-head sites which were at one time considered uneconomical. It became, therefore, increasingly important to find methods of measuring the discharge of low-head plants where the water quantities are large and the water passages particularly short and unsuited to other methods of testing. American engineers had developed methods of measurement of flow in long penstocks and then attempted to extend these methods to plants with shorter water passages. European engineers have shown a preference for current meters, at one time commonly used on both sides of the Atlantic for measurements in large intakes. The paper discusses the status of the current-meter method in Europe at the time this method was selected for the tests at Safe Harbor and the application of the two-type meter method. It shows how this method was applied at the outset and how certain modifications were made for increasing the reliability and decreasing the time and effort required for making tests. These made possible new methods of compilation which have been developed to facilitate greatly this phase of the testing program. The successful application of these methods should make current-meter measurements more feasible than ever before. In preparation for these tests, investigations were conducted at the Bureau of Standards and elsewhere to determine the characteristics and limitations of the meters under various conditions of uniform, oblique, pulsating, and turbulent flow. It has been shown that water passages with parallel sides for metering and approach sections do not insure parallel flow, and that even under as nearly ideal conditions as it is practical to secure, the use of two types of meters will indicate an effective angularity. However, it is believed that accurate measurements of oblique flow can be made by the use of two types of meters, each affected to a different extent by angularity. The use of this method will greatly enlarge the field of current-meter testing. There are pointed out the advantages of making index tests in conjunction with current-meter measurements; not only to extend them to a wide range of operating conditions, but also as a measure of the consistency of the discharge measurements.

Concerning the Degree of Accuracy of the Gibson Method of Measuring the Flow of Water

Abstract The paper first discusses the limitations of various methods of measuring water which were in use when the Gibson method was first announced. These limitations of the current-meter method of flow measurement include: The effect of turbulent accessory motions which cause periodic velocity changes in the direction and magnitude of flow; the difficulty in obtaining readings close to the wall of the canal or closed conduit; and the necessity of determining the velocity at several points simultaneously due to temporary changes in distribution; and the expense involved in taking a number of such simultaneous readings. Reference is also made to the use of the pitot tube for taking readings close to the wall of the passage. The greater part of the paper, devoted to a discussion of the Gibson method of water measurement, includes the derivation of formulas involved in this method of water measurement, its limits of accuracy, and the errors which may arise in its use. These errors, due to (a) accessory motions, (b) to false valuation of friction, (c) to friction of the mercury column, and (d) to inertia of the mercury column, are presented with derived formulas and approximate values together with suggestions for minimizing them.