Fast And Accurate Numerical Simulation Of Non-equilibrium Wet Steam Flows

Dongyang Zhang (Engineering Thermophysics)Directed by Hongde JiangA fast and accurate numerical method for non-equilibrium wet steam flow (FAWS) is developed in this thesis. The relative saturation wetness (transition function) is defined and the approach by distinguishing different thermal property zones is developed. The generated thermal property tables of steam are applied in numerical simulation to accelerate calculation. Analytical Wilson point parameters are calculated to calculate the intensly nucleating location and the dynamic calculation of limiting supercooling degree with iteration process is developed to obtain the accuracy of this location. The simulation of intense nucleation time as the function of pressure and expansion rate is made. The divergence expression of expansion rate is proposed and the calculation of expansion rate by flux integral is developed successfully. It is especially suitable for finite volume method. The periodic boundary condition under the condition that dry and wet steam co-exist is kept for the flow after the trailing edge of blade by the averaging of transition function on periodic boundary and the second calculation of transition function. FAWS is developed and applied in S1 flow numerical simulation program firstly. The nucleating flows in Laval nozzle and 2D turbine cascade are simulated. By comparison with experimental data, good agreement between calculated and experimental surface pressure is obtained and the distributions of many flow parameters are displayed. The comparison between the calculation results by FAWS and by solving droplet number and radius equations shows that the accuracy of FAWS is high enough to satisfy the need of engineering and scientific research. The distributions and functions of the parameters related to nucleating flow are also analyzed.FAWS has been developed for 3D viscous wet steam flow calculation and the functions of equilibrium condensation and dry flow calculation are also developed in the thesis. The flow in an initial condensation stage of low-pressure cylinder of a 200MW steam turbine is analyzed and the phenomena of non-equilibrium condensation are captured. The distributions and influences of parameters of 3D condensation flow are analyzed and valuable conclusion for the design of blade is drawn. Transition function equation method for the simulation of wet steam flow is also developed and analyzed.The investigation on the theory of homogeneous condensation is also made in this thesis. The spatial sequence of Wilson point, minimum pressure point and minimum temperature point is derived and the non-coincidence of these three pointsis proved for the first time. The expression of wetness for the zone near Wilson point and the accurate exponent expression of wetness for minimum pressure point are obtained. Two sets of algebraically explicit analytical solution are derived for the partial differential equation set describing the one-dimensional unsteady gas-liquid two-phase flow. In this thesis, the characteristics of tabulating thermal properties of water steam are investigated and two kinds of tables are developed and applied for numerical calculation. The high efficiency and accuracy of these tables and corresponding interpolation program are attained. A numerical program for one-dimensional nucleating flow by the fourth order Runge-Kutta scheme is also developed and slip factor B is introduced to simulate the flow when the velocity difference between two phases exists. The formula of critical droplet radius for which real gas property and volume of liquid phase are considered is derived from two different ways.