Charles C. S. Song

Evaluation of pedestrian winds in urban area by numerical approach

Abstract A large eddy simulation CFD model based on the weakly compressible flow equations has been used to simulate the pedestrian wind fields around urban area. This paper presents some practical examples of the CFD model applications to environmental wind evaluation. Since numerical model can provide the detailed wind flow data at every grid points and every time step at different wind conditions, it has a great advantage over wind tunnel test to accurately evaluate the wind effects on pedestrian and other environmental issues. Furthermore, advanced computing technology has made the numerical modeling become fast and cheap. Currently, a typical case of the examples can be completed within 2–3 weeks. It is believed that the CFD method is now a feasible tool of wind engineering.

Computation of three-dimensional flow around square and circular piers

The aim of the present study is to investigate, by numerical simulation, the three-dimensional turbulent flow field around square and circular piers. The numerical model employs a finite volume method based on MacCormacks explicit predictor–corrector scheme to solve weakly compressible hydrodynamic equations for turbulent flow. Computed results are compared with Dargahis experimental measurements to assess the validity of the proposed model. Very good agreements are obtained. The results of flow simulation indicate that near the upstream face of the pier there exists a downflow, which joins the separated flow to form the horseshoe vortex stretched around the pier. This horseshoe vortex interacts with the wake vortex to create the upflow behind the pier. These phenomena appear to be very important to the mechanism of scouring around the pier. In general, the flow patterns for the square and circular piers are similar. However, the strengths of the downflow and horseshoe vortex are greater in the case of the square pier. The position of the horseshoe vortex around the circular pier is closer to the front face than that around the square pier. In the meantime, the domain of the wake flow in the case of the square pier is greater than that in the case of the circular one. Copyright

Computation of wind flow around a tall building and the large-scale vortex structure

Abstract A numerical study of three-dimensional wind flow around a tall building is presented in this paper. The solution is obtained by solving weakly compressible flow equations, along with Smagorinskys subgrid-scale turbulent model. The numerical scheme is based on MacCormacks predictor-corrector explicit finite volume method. First, the numerical model was verified by testing a shear flow around surface-mounted cube, then a detailed study was carried out for a shear flow around a taller building model (width:length:height = 1:0.889:4.667). The main task of this paper is to explore the large-scale vortex structure and the unsteady behavior of flow around a tall building, which are still not well understood.

A numerical study of wind flow around the TTU building and the roof corner vortex

Comprehensive studies on wind flow around the TTU (Texas Tech University) building were conducted in both field test and wind-tunnel modeling. The results are very useful benchmark database for computational wind engineering studies. Therefore, a number of numerical studies have been carried out since then to explore a deeper insight into the physical nature of the flow characteristics. However, the previous numerical studies have not reported much about the results on the roof corner vortex, which is believed to be very important in engineering applications. This paper presents a recent numerical study of wind flow around the TTU building using an advanced CFD method with large eddy simulation approach. The main focus of this paper is the roof corner vortex. Two approaching wind directions (215° and 225°) to the building were investigated with three mesh systems. The three-dimensional roof corner vortex pattern is successfully simulated. The mean values are generally in good agreement with the wind tunnel modeling and field test, but the rms values are not comparable since the numerical results only include the resolvable part due to the large-scale eddies while the small-scale eddies are modeled by SGS model and not included in the comparison. However, as the mesh system is made finer, the rms values are closer to the measured data since more smaller scale eddies are directly resolved.

Simulation of Flow Through Francis Turbine by Les Method

The traditional approach of Francis turbine design which is based on the steady potential flow theory and heavily dependent on model testing and engineering experience, has come a long way in producing efficient and relatively cavitation free turbines. But further improvement of performance for design and off design operating conditions will be extremely difficult with the traditional method because it will depend more on those phenomena such as, boundary layer separation, vortex dynamics, interactions between different components, vibrations, etc., which are not predictable with conventional approach and difficult to measure in physical models.

The effects of submergence on structural response in confined pools

Abstract In this paper the response of single and multi degree of submerged systems is investigated. The complete equations of motions including fluid coupling terms are developed for submerged bodies where the surrounding fluid is both moving in phase and out of phase with the support motion. The analysis considers both structural and fluid damping. Also included is an analysis of two degrees of freedom fluid coupling for submerged bodies completely enclosed within another body. In this case limiting conditions of the inner body hydrodynamic mass are examined, along with the frequency response characteristics of these systems. The paper developes a simplified forcing function approach for in phase fluid support motion systems. This method is applicable for both modal-spectral and time history dynamic analyses of any linear structure. The results of the analysis are expanded for structures with non-linear support configurations, i.e., (sliding or rocking bases) to again define a simplified analytical approach accounting for in phase fluid support motion.

Simulation of Flow Through Pump-Turbine

For years Francis — type reversible pump — turbines have been applied to many pumped storage power plants over the world. So far, they have been used under peak shaving generating operation with AFC (automatic frequency control) function during daytime, and plain pumping — energy consuming — operation at night time. Recently, an adjustable speed pump — turbine was realized in Japan. It begins to add a remarkable AFC function in pumping mode to the conventional pump-turbines.

The Role of Energy Dissipation in Fluid Flows and River Mechanics

Based on the theory of irreversible thermodynamics and a number of numerical and experimental examples of fluid mechanics and water resources, energy dissipation has been shown to be the primary stabilizing force that determines the direction of change towards an equilibrium condition. Possible future research directions on the use of energy methods in dealing with complex water-resources related problems are suggested.