Hu Chunbo

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.

A numerical study of bingham turbulent flow in sudden-expansion straight circular pipe

The control equations for the turbulent flow of Bingham fluid are established according to Bingham fluid constitution equation. Pressure field and velocity field are correlated by pressure-correction equation. The numerical computations are performed on Bingham fluid turbulent flow in sudden-expansion straight circular pipe, and the flow mechanisms are discussed.

K-ε-T model of dense liquid-solid two-phase turbulent flow and its application to the pipe flow

To predict the characteristics of dense liquid-solid two-phase flow, K-ε-T model is established, in which the turbulent flow of fluid phase is described with fluid turbulent kinetic energy Kf and its dissipation rate ɛf, and the particles random motion is described with particle turbulent energy Kp and its dissipation rate ɛp and pseudothermal temperature Tp. The soverning equations are also derived. With K-ε-T model, numerical study of dense liquid-solid two-phase turbulent up-flow in a pipe is performed. The calculated results are in good agreement with experimental data of Alajbegovic et al. (1994), and some flow features are captured.

Effect of empirical coefficients on simulation in two-scale second-order moment particle-phase turbulence model

A two-scale second-order moment two-phase turbulence model accounting for inter-particle collision is developed, based on the concept of particle large-scale fluctuation due to turbulence and particle small-scale fluctuation due to collision. The proposed model is used to simulate gas-particle downer reactor flows. The computational results of both particle volume fraction and mean velocity are in agreement with the experimental results. After analyzing effects of empirical coefficient on prediction results, we can come to a conclusion that, inside the limit range of empirical coefficient, the predictions do not reveal a large sensitivity to the empirical coefficient in the downer reactor, but a relatively great change of the constants has important effect on the prediction.