Applied Mechanics and Materials Vols. 444-445

Abstract: Taking a pumping station project with large scale centrifugal pumps as working example, an extreme transient flow in the pumping system caused by tripping pump due to electric supply failure was analyzed, and hydraulic disturbance or impulsion to the rest working running pumps were investigated by using the software of the Deltares WANDA 3.73. The results show that the rest running pumps in the system due to a sudden tripping pump disturbance are heavy disturbed when the tripping pump is suddenly failed from the pumping system. The flow rate and input power for the working pumps are greatly jumped shortly. The strongly transient impulsion to the pumping system is quite significant.

Abstract: Although there are some achievements of flow-induced vibration of plane steel gate, few is about the influence on gate caused by the difference of structure types of gates hemline. This paper studies on the flow pattern, natural vibration characteristics and dynamic response of four typical types of gates hemline in deep hole of Kajiwa Hydropower Stations service gate. Based on model test and numerical simulation and considering the flow pattern under the gate and in the gate slot, the natural vibration characteristics and the gates dynamic response, it is suggested to use an anteversion angle and a caster angle (type D for short) for the hemline of the type II gate slot. The optimal factors of a gates hemline in a concrete project can be optimized by numerical simulation.

Abstract: Computational fluid dynamics were used to study the three-dimensional unsteady flows in a closed pipeline system with a screw-type centrifugal pump during rapid starting period. The unsteady Reynold time-averaged Navier-Stokes equations, RNG have been used to solve the unsteady, incompressible, viscous turbulent effects. The sliding mesh technique is proposed to resolve the transient flows caused by the started impeller. Combined with the characteristics of the motor, the screw-type centrifugal pump was started by two different way of linear and exponential acceleration. The automatic update of the rotational speed variation of field around the impeller was realized by FLUENT UDF. The transient variation of the pressure at the pump inlet and outlet, the global performance characteristics and the transient flow evolutions were obtained under different start-up modes. The results show that the rapid starting period presents obvious transient effect; the transient head, power curves changing with time reveal the transient attachment head and additional power part. Compared with the linear mode, the transient flow, shaft power, efficiency tend to a steady state value within a relatively short period in setting start time and maintain a quasi-periodic fluctuations.

Abstract: The unsteady flow around a triangle cylinder was simulated using the multiscale turbulence model based on the variable interval time average method. The numerical method used in this simulation is an unstructured staggered mesh scheme. The computational results show that the multiscale turbulence model can successfully simulate vortex shedding characteristics. The Strouhal number and time-averaged velocity profiles also agree better with experiments than that of the standard k-ε model.

Abstract: The effect of steps in the line search on the consistence of adjoint-based drag reduction of airfoil is investigated in this paper. Constant step adopted in drag reduction design usually gives different optimization results and choice of constant step often depends on designers experience and optimization problem. Bracket method is applied to automatically give the optimal step in performing drag reduction design of airfoils RAE2822 and S73613 and the consistent optimal results are obtained. The results illustrate that the linear search method can automatically find the optimal step, and overcome the restriction on choice of user-defined constant step which is used in the traditional adjoint-based optimization method. That is, it reduces the dependence of step in the drag reduction design, and improves the robustness of the adjoint-based airfoil drag reduction optimization design method.

Abstract: Based on the three-dimensional incompressible Navier - Stokes equations and the standard turbulent model, this paper develops a tunnel-air-train simulation model. Time-history variation rules and space distribution characteristics of train wind are studied at 200km per hour, and safety avoidance distance on evacuation passageways is further discussed. The results show that: Train wind is complex three-dimensional flow which is changed with time and space, since personnel safety may be threatened by train wind. Therefore, effective measures should be taken to avoid accidents.

Abstract: A DDES (Delayed Detached-Eddy Simulation) method is presented and applied to simulation and design of a CFJ (Coflow Jet) airfoil at high angle of attack. The method is based on average vorticity, and is used to predict a number of test cases, including a circular cylinder flow, vortex design and simulation of the CFJ airfoil. The results demonstrate that the DDES method is efficient for CFJ airfoil flow. It provides reference to flow control and aircraft design.

Abstract: The highway tunnel is a relatively closed space, then large amounts of motor vehicle exhaust emissions, especially CO, resulting in air pollution in tunnel. The project construction cost, operation cost, and pollutant concentration distribution in tunnel are most dependent on ventilation scheme. Usually have air extraction and inflatable type ventilation system. In this paper, a numerical simulation based on two-phase flow is used to study the effect of double air extraction ventilation system to CO concentration distribution in large tunnel. The method can effectively track the gaseous diffusion and the results show that the CO concentration is lowest in the middle area of two vents and the exit area of tunnel. The highest area of CO concentration located in vents below area and the middle area of tunnel.

Abstract: The vibration intensity is strong in Francis turbine occurred under the small opening conditions, such as Lijia Gorges and Three Gorges project. In paper we use large eddy simulation (LES) method base on Vreman SubGrid-Scale model to study the generation and evolution process of turbulence flow, capturing the details of the flow structures and the dissipation of the turbulent kinetic energy. The SIMPIEC algorithm is applied to solve the coupled equation of velocity and pressure. The result shows that the small guide vane opening conditions deviate the optimal conditions most. So some unstable flow characters been induced. Such as the turbulent kinetic energy of fluid in guide vanes zone, the blade passage and the draft tube are very strong. The unstable flow phenomenon including the swirl, flow separation, interruption and vortex strip. It can be deduced that the vibration of unit is induced by these flow characteristic.

Abstract: The effect of slender body on the rolling characteristics of a double delta wing is found by comparing the numerical simulation results of the double delta wing and wing-body configuration. The coupled computation system solving the Navier-Stokes equations and the rolling motion equation alternatively to obtain the unsteady vortical flow around the two configurations while rolling. The results conclusively showed the upwash effect of the slender body enhanced the energy of strake vortex and merged vortex.The aerodynamic lag of double delta wing is weak, contrarily, the time lag effect of the wing-body configuration is significant. The asymmetry vortices structure nearby the trailing edge are believed to be the main reason for the unsteady time lag effect.