Cai Ti-min

Droplet Collision and Coalescence Model

A new droplet collision and coalescence model was presented, a quick-sort method for locating collision partners was also devised and based on theoretical and experimental results, further advancement was made to the droplet collision outcome. The advantages of the two implementations of smoothed particle hydrodynamics (SPH) method were used to limit the collision of droplets to a given number of nearest droplets and define the probability of coalescence, numerical simulations were carried out for model validation. Results show that the model presented is mesh-independent and less time consuming, it can not only maintains the system momentum conservation perfectly, but not susceptible to initial droplet size distribution as well.

Difference scheme for two-phase flow

A numerical method for two-phase flow with hydrodynamics behavior was considered. The nonconservative hyperbolic governing equations proposed by Saurel and Gallout were adopted. Dissipative effects were neglected but they could be included in the model without major difficulties. Based on the opinion proposed by Abgrall that “a two phase system, uniform in velocity and pressure at t=0 will be uniform on the same variable during its temporal evolution”, a simple accurate and fully Eulerian numerical method was presented for the simulation of multiphase compressible flows in hydrodynamic regime. The numerical method relies on Godunov-type scheme, with HLLC and Lax-Friedrichs type approximate Riemann solvers for the resolution of conservation equations, and nonconservative equation. Speed relaxation and pressure relaxation processes were introduced to account for the interaction between the phases. Test problem was presented in one space dimension which illustrated that our scheme is accurate, stable and oscillation free.

Instantaneous Regression Rate Computation of Hybrid Rocket Motor Based on Fluid-Solid Coupling Technique

[Abstract] A model that is based on the complex physical and chemical processes in the operation of hybrid rocket motor and able to work in different operating conditions, was proposed to predict the flow characteristics and fuel grain pyrolysis surface regression rate in hybrid motors. Navier-Stokes equations coupled with chemical species and turbulence transport equations were applied to simulate unsteady turbulence gas flow in the passage. The equation set was complemented by an additional turbulent model. A low-Reynolds number e − k turbulent model was used to decrease the instability of the heat transfer near the grain surface. The coupling between the solid and gaseous phases was carried out through energy and mass conservation on the interface. Dynamic mesh techniques were used to simulate moving process of the grain surface. The dynamic mesh update methods used in the paper are Spring-Based Smoothing Method and Local Re-meshing Method. The model was validated by comparison between computational and experimental data, and then was used to simulate a lab-scale hybrid rocket motor. Temperature, velocity, and species distributions were obtained, as well as the temperature and regression rate on the grain pyrolysis surface.

Computation of Supersonic Turbulent Flowfield With Transverse Injection

Three dimensional steady flowfield generated by transverse sonic injection into a supersonic flow was simulated by solving the Favre-averaged Navier-Stokes equations using the weighted essentially nonoscillatory (WENO) schemes and Jones-Launder k-ε model. Results indicate that in the upstream of the square injection there exist two main recirculation regions and the primary vortex induces the horseshoe vortex region. In the downstream there is a low pressure region which conduces a pair of helical vortex.

An implicit algorithm of thin layer equations in viscous, transonic, two-phase nozzle flow

Omitting viscosity along flow direction, we have simplified the dimensionless N-S equations in arbitrary curved coordinate system as the thin layer equations. Using the implicit approximate-factorization algorithm to solve the gas-phase governing equations and the characteristic method to follow the tracks of particles, we then obtained the full coupled numerical method of two-phase, transonic, turbulent flow. Here, particle size may be grouped, the subsonic boundary condition at entry of nozzle is treated by quasi-characteristic method in reference plane and the algebraic model is used for turbulent flow. These methods are applied in viscous two-phase flow calculation of rocket nozzle and in the prediction of thrust and specific impulse for solid propellant rocket motor. The calculation results are in good agreement with the measurement values. Moreover, the influences of different particle radius, different particle mass fraction and particle size grouped on flow field have been discussed, and the influences of particle two-dimensional radial velosity component and viscosity on specific impulse of rocket motor have been analysed.The method of this paper possesses the advantage of saving computer time. More important, the effect is more obvious for the calculation of particle size being grouped.