Applied Mechanics and Materials Vols. 444-445

Abstract: Incorporating the ITS in traffic flow, two lattice hydrodynamic models considering the following lattice are proposed to study the influence of the following lattice on traffic flow stability. The results from the linear stability theory show that considering the following lattice could lead to the improvement of the traffic flow stability. The modified Korteweg-de Vries equations (the mKdV equation, for short) near the critical point are derived by using the nonlinear perturbation method to show that the traffic jam could be described by the kink-antikink soliton solutions for the mKdV equations.

Abstract: Dynamic stall can delay the stall of wings and airfoils that are rapidly pitched beyond the static stall angle. A new method of active dynamic stall control by the undulatory foil was proposed in this paper. The study was based on solving unsteady Reynolds-Average Navier-Stokes equations. Comparisons of the effectiveness of pitching foils and undulatory foils on dynamic stall control in both light stall and deep stall were conducted. The undulatory foils with various controllable parameters were further discussed. The results showed that the performance of undulatory foils is much better than that of the rigid pitching foil at high angles of attack either in the light stall or in the deep stall situation.

Abstract: In order to predict the flush performances of digital toilet products before mass production, a numerical simulation for a three-dimensional unsteady multi-phase flow in the flushing process of a wash-down toilet is carried out by using FLUENT software. The finite volume method (FVM) is used to discrete the three governing equations in space and time. The discrete equations are solved by using the first-order upwind discretization scheme and the PISO pressure-velocity coupling scheme. The realizable turbulence model is chosen as the viscous model to treat the fluid flow with large bending curvature wall. The volume of fluid (VOF) model is applied to solve the transient free-surface problem. First, a two-phase flow was simulated on the assumption that there is not sewage but water in the trap seal. Then, by simplifying the mixture of sewage and water in the trap seal as the third phase with high viscosity, a three-phase flow was simulated. Moreover, in order to validate the simulated results, a flushing testing was conducted to test the flush range, and a target type flow meter was designed, calibrated and applied to test the flush velocity. The comparisons show a good agreement between the numerical and experimental results. Based on the verified simulation results, the flush performances of the digital wash-down toilet, such as flush range, flush velocity and sewage replacement ability, can be predicted and evaluated.

Abstract: When the buried high pour point oil pipeline is running, it is inevitable to avoid pipeline failures and the pipeline should be shutdown. After shutdown oil temperature dropped and viscosity increased, oil gelling happens, it will cause the accident "condensing tube". For high pour-point oil pipeline can start after shutdown, it should ensure the safety shutdown time of the pipeline and corresponding in the restart pressure. So it is necessary to guide the production practice and pipeline safe operation.

Abstract: GPGPU has drawn much attention on accelerating non-graphic applications.A new algorithm on the numerical simulation of Lattice-Boltzmann method (LBM) based on CUDA is studied.The cavity flow is simulated by D2Q9 model of LBM method ,with the non-equilibrium extrapolation method for velocity boundary to deal the wall boundary conditions and using global memory and texture memory to store data.In the model the 9 distribution functions were all stored in the form of two-dimensional grid, each grid is assigned a thread and each thread block includes 256 threads.The simulation for cavity flow with LBM was carried out by CUDA and NVIDIA GeForce 8600 GT on a PC.The speed is more than 15 times faster than that of the CPU.

Abstract: In this paper, computational fluid dynamics calculations were conducted under various kinds of complex working conditions for rotating long orifice. As one of the most important structures of throttling and pressure limiting, orifice plays a significant role in flow control of the whole system. The existing empirical correlation was improved by correction on characteristics of low Reynolds number and compressibility. Then, improved one-dimensional analytical model of rotating long orifice with chamfered or radiused inlet was developed by programming. The model was verified against the results of commercial computational fluid dynamics codes. It turns out that the model has high precision, excellent convergence, and can predict the flow parameters under working conditions of low Reynolds number, supersonic and high pressure ratio with an acceptable error. And only geometric features, rotational speed and boundary conditions are required for one-dimensional modeling. Thus, it can be applied in the one-dimensional calculation and design of secondary air system widely.

Abstract: Supersonic swirling separator had a good ability in separating gas-liquid. In this paper, the Laval-nozzle and straight-tube of the non-central cone supersonic swirling separator were optimized designing. The separation performance of the optimized supersonic swirling separator was researched by CFX. The results show that,with the relative pressure ratio decreasing, the shock waves which occurred in the diffuser moved towards the extraction device, the maximum Mach number decreasing. When the relative pressure ratio down to 1.4, the outlet total pressure recovered to 73% of the inlet total pressure, the flow in the divergent section of Laval-nozzle and the straight-tube was supersonic, the lowest temperature can be down to-84.5°C and the maximum centrifugal acceleration was 261,800g, which provided a swirling and cold environment for the separation of gas-liquid; With the straight-tubes length-diameter ratio increased, a normal shock wave occurred in the straight-tube. Further increased the length-diameter ratio, the normal shock wave moved towards the throat and the strength of the shock wave was increasing, which was a disadvantage to the separation of the gas-liquid.

Abstract: Low permeability reservoirs have abundant reserves, accounting for about one-third of all the reservoir storage, but the development is difficult and the recovery is low because of its poor natural property. Reasonable well pattern, well pattern parameters and fracture parameters can be effective in improving the development of low-permeability reservoir. Therefore, studying flow law of various well networks, choosing a reasonable well pattern and corresponding well parameters, are key issues of cost-effective development of low permeability reservoir. Based on extensive investigations of former researches, this paper studies the flow law of vertical well patterns and the effect of permeability differential on flow law. Adaptive study of those different kinds of well patterns has been done by numerical simulation method, including the five point well pattern, inverted seven point well pattern and the inverted nine point well pattern. Studying the typical horizontal well pattern on the flow law, comparing the characteristics of the streamlines. Choosing a reasonable form of well pattern and the well pattern parameters.

Abstract: A grid fin is an unconventional lifting and control surface which consists of an outer frame with an inner grid of intersecting planar surfaces of small chord. Normal shocks form at the back of the lattice cells at transonic Mach numbers thus choking the flow through the cells and causing a significant reduction in lift force and increase in drag force. An improved circular-arc grid-fin configuration is proposed in the present study to reduce transonic flow choking. Viscous computational fluid dynamic simulations were performed to investigate flows over single baseline and circular-arc grid fins and body-fin configurations under transonic and supersonic flow with Mach numbers in the range of 0.6-4.0. The present numerical results indicate the drag coefficient on single circular-arc grid fin and body-fin configuration is decreased by approximately 10%-24% and 8% respectively for all the Mach numbers investigated in the present study.

Abstract: According to the TTCP geometry, change the wrap-around fins to the planar fins. Construct the flow-field then generate the grid. Utilizing the computational fluid dynamics method, the lift, drag and roll moment coefficients are computed in different angles of attack. The roll moment coefficients are computed from the flow field solution and compared with the experimental results. The results show good agreement with the experimental measurements for various flight Mach numbers. The aerodynamic characteristics of these two fins are similar to each other from the numerical solution. If consider the lift, drag and center of pressure coefficients merely, these two kinds of fins can be interchanged .But the roll moment coefficient in Wrap-Around fins and planar fins are different. They need to calculate separately.