The New Semi-Experimental Method for Simulation of Turbine Flow Meters Rotation in the Transitional Flow
The new semi-experimental method for simulation of the turbine flow meters rotation in the transitional flow has been developed. The method is based on the experimentally established exponential low of changing of dimensionless relative turbine gas meter rotation frequency and meter inertia time constant. For experimental evaluation of the meter time constant special facility has been developed. The facility ensures instant switching of turbine meter under test from one channel to the other channel with different flow rate and measuring the meter response. The developed method can be used for evaluation and predication of the turbine meters response and dynamic error in the transitional flow with any arbitrary law of flow rate changing. The examples of the method application are presented. Keywords—Dynamic error, pulsing flow, numerical simulation, response, turbine gas meters.
Turbine flowmeter response to transitional flow regimes
Abstract In this paper, acceleration and deceleration performance of turbine flowmeters was investigated in transitional flow regimes. Different flow meters and peak gas flow rates were used, with a step flow transition induced by rapid closing and reopening of the pipeline valve. Hotwire anemometry was employed as a reference method to assess the dynamic response of turbine flowmeters. Results of this study suggest a good dynamic response of turbine flowmeters in accelerating flows, with only a slight delay of the turbine rotation. However, in decelerating flows, the response of the flowmeter turbine was found to be slow, with characteristic time constants up to 35 s and large resulting over-registration of transferred gas volume. Our findings were quantified by multiple regression models for flowmeter response times and over-registered volumes, which were both find to drop with Reynolds number and increase with the flowmeter size. Understanding dynamic response is essential to evaluate dynamic errors and evaluate overall measurement uncertainty.
Dynamic response of small turbine flowmeters in pulsating liquid flows
The dynamic response of turbine flowmeters in low pressure gas flows (i. e. where the rotational inertia of the fluid is negligible) is well understood and methods for correcting meter signals for a lack of response are available. For liquid flows there has been a limited amount of experimental work on the response of meters to step changes but no reports have been found of the response of meters to sinusoidally pulsating flows. "Small" turbine meters are expected to behave differently from "large" meters for a number of reasons: a smaller meter would generally have: (1) a larger percentage of tip clearance leakage flow; (2) less fluid momentum between the meter blading; and, (3) less fluid friction forces on the effective surface area. In this research, arbitrarily, meters up to size 25 mm were defined as small; and within this study, meters of size 6 mm to 25 mm were investigated. The aim of the research was to investigate and to understand the response of small turbine meters to pulsating liquid flows and to provide methods for correction. Three approaches were used: (1) application of an existing theoretical model of turbine meter behaviour; (2) an experimental investigation of meter performance in pulsating flows; and (3) simulation of flow behaviour through one selected meter using CFD and extending the simulation to predict the rotor dynamics and, hence, the response of this meter to specified cases of pulsating flow. A theoretical model developed by Dijstelbergen (1966) assumes frictionless behaviour and that flow is perfectly guided by meter blading through the rotor and that fluid within the rotor envelope rotates as a "solid body". Results from this theoretical model applied for pulsating flows showed that there was likely to be positive error in predicted mean flow rate (over-registration) and negative error for predicted values of the amplitude of the pulsations (amplitude attenuation). This behaviour is due to the fundamental asymmetry between flows with increasing and decreasing angle of attack relative to the meter blades, throughout a pulsation cycle. This qualitative behaviour was confirmed by experimental work with meters up to size 25mm working with pulsation frequencies up to 300 Hz. For low frequency pulsations