| Two phase flow is ubiquitous in the industrial pipeline, such as the heat exchanger. Here, it is necessary to put forward the manifold states are divided into gas-liquid two-phase flow, gas-solid two-phase flow, liquid-liquid two-phase flow and liquid-solid two-phase flow. This paper is mainly about the gas-liquid two-phase flow.Gas liquid two-phase flow widely exists in industrial areas, for example a small amount of liquid will be carried in the natural, the steam will be partial liquefied with temperature decreased. Vortex pressure field will be damaged due to the liquid phase action. The measurement error caused by using single phase vortex flowmeter to measure two phase flow rate. Turbulent of the flow field is enhanced with void fraction increased, leading to the gas phase vortices reduction, vortex signal gradually weakened, the worse-case scenario is vortex signal completely submerged in the turbulent fluctuation. The phenomenon only exists in the multiphase flow conditions that vortex signal disappeard with liquid holdup the increased, which increases the complexity of two-phase flow measurement using vortex flowmeter. Calculation model of vortex flowmeter for single phase flow is not suitable for flow rate measurement in two phase flow, but there are few papers involves the vortex street characteristics in gas-liquid two-phase flow.This issue focuses on the characteristics of vortex flow meter in gas-liquid two-phase flow, and mainly includes the following works:(1) Based on Biot-Savart Law and Single-phase flow Karmon Vortex characteristics, flow field has been analyzed when gas-liquid flow past a fixed bluff body with low liquid holdup. To discuss the relation between liquid holdup and vortex signal intensity, this paper sets up vortex-induced pressure field model for gas-liquid two-phase flow, gives the formula for decay rate of vortex signal. Vortex signal characteristics have been studied for stratified two phase flow on atmospheric conditions in horizontal pipe.(2) Fluctuant pressure coefficient is presented as an index of vortex energy of the wake behind a bluff body in mist flow. Calculation for vortex energy is obtained from inter-phase force analysis, based on Basset-Boussinesq-Oseen equation and conservation of mechanical energy. Vortex energy is weakened by liquid disturbance, the relationship between the fluctuant pressure coefficient and liquid velocity is set up on theory analysis. An existence criterion for vortex streets is proposed using the relationship. A new algorithm for prediction of liquid velocity is put forward.(3) The simultaneous equations of orifice plate and vortex flowmeter is established for meter the flow rate of gas-liquid two-phase flow. The conversion relationship between the vortex frequency and gas volume flow is set up through theoretically analysis, considering the effects of parameters, such as void fraction, droplet entrainment ratio and gas-liquid two-phase slip, and the existence of the velocity profile and other physical phenomenon.(4) Parameters-induced stochastic resonance base on spectral entropy(PSRSE) is put forward to detect weak signal. Parameters are adjusted by spectrum entropy of weak signal to obtain the optimal effect of stochastic resonance. After processed by PSRSE, weak signal amplitude has been amplified and noise has been suppressed, so the frequency could be gotten even if it drowned in noise.Vortex signal has been detected by PSRSE, and results show that vortex frequency in some undetectable point could be identified after PSRSE, which confirmed the ability of PSRSE on weak signal detection. |
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