**6. Conclusion**

In this study, we performed LES of turbulent flow and plume dispersion around a cubical building and investigated the basic performance of the LES model in comparison with experimental data of Sada & Sato., (2002), Sato and Sato., (2002). The scheme to generate a spatially-developing turbulent boundary layer flow in the driver region was proposed by incorporating an existing inflow turbulence generation method into an upstream small fraction of the driver region with a tripping fence placed at the ground surface. With this scheme, we successfully simulated a turbulent boundary layer flow corresponding to that in wind tunnel experiments of Sada & Sato., (2002) in the driver section. The findings implied that our LES model could simulate various types of wind tunnel flow by incorporating the existing inflow turbulence generation method and moderately setting up roughness obstacles in the driver region.

Turbulence intensities behind a cubical building around the building height were slightly overestimated in comparison with experimental data of Sada & Sato., (2002). However, the main characteristics of turbulent flow such as a sharp peak behind the building and the formation of a uniform turbulent flow field with downstream distance, corresponding to the wind tunnel experiment, are obtained. Also, dispersion characteristics such as a sharp peak close to the point source and the formation of concentration profiles with downstream distance were successfully simulated in comparison with the experimental data. These indicated that the difference in turbulence characteristics between the experiments and our LES model was not significant. The basic performance of our LES model for turbulent flow and dispersion fields could be recognized as comparable to the wind tunnel experiment.

Dependence of the patterns of probability distributions of concentration fluctuation of the LES model on the values of concentration fluctuation intensity were consistent with those of the wind tunnel experimental results of Sato & Sada., (2002). Focusing on various peak concentration ratios, we saw c90/c' and c99/c' values of the LES model were in good agreement with the experimental data. From these facts, we considered that the occurrences of high concentrations were captured by our LES model. From the above results, we considered that the basic performance of our LES model was almost comparable level to that obtained by the wind tunnel experimental techniques.

Here, we discuss the applicability of the present LES model for flow and dispersion around an isolated building to the problem of plume dispersion within a group of buildings. Within an urban canopy, three typical flow patterns, isolated flow, wake interference flow and skimming flow within building arrays are formed depending on the ratio of the buildings height to the street width and the flow filed is highly complex (Oke., 1998). Considering a surface geometry of urban canopy is composed of a group of isolated buildings and obstacles, numerical simulation with moderate grid points for each building and obstacle can capture such complex flow patterns with reasonable accuracy. Therefore, from the validation of our LES model for turbulent flow and plume dispersion around an isolated building, it is considered that the present model with moderate grid points for each building can apply to a simulation of plume dispersion within urban canopy.

### **7. References**

Csanady, G.T. (1973). *Turbulent Diffusion in the Environment*, D.Reidel Publishing Co., Dordrecht, Holland, 222-248

In this study, we performed LES of turbulent flow and plume dispersion around a cubical building and investigated the basic performance of the LES model in comparison with experimental data of Sada & Sato., (2002), Sato and Sato., (2002). The scheme to generate a spatially-developing turbulent boundary layer flow in the driver region was proposed by incorporating an existing inflow turbulence generation method into an upstream small fraction of the driver region with a tripping fence placed at the ground surface. With this scheme, we successfully simulated a turbulent boundary layer flow corresponding to that in wind tunnel experiments of Sada & Sato., (2002) in the driver section. The findings implied that our LES model could simulate various types of wind tunnel flow by incorporating the existing inflow turbulence generation method and moderately setting up roughness

Turbulence intensities behind a cubical building around the building height were slightly overestimated in comparison with experimental data of Sada & Sato., (2002). However, the main characteristics of turbulent flow such as a sharp peak behind the building and the formation of a uniform turbulent flow field with downstream distance, corresponding to the wind tunnel experiment, are obtained. Also, dispersion characteristics such as a sharp peak close to the point source and the formation of concentration profiles with downstream distance were successfully simulated in comparison with the experimental data. These indicated that the difference in turbulence characteristics between the experiments and our LES model was not significant. The basic performance of our LES model for turbulent flow and dispersion fields could be recognized as comparable to the wind tunnel experiment. Dependence of the patterns of probability distributions of concentration fluctuation of the LES model on the values of concentration fluctuation intensity were consistent with those of the wind tunnel experimental results of Sato & Sada., (2002). Focusing on various peak concentration ratios, we saw c90/c' and c99/c' values of the LES model were in good agreement with the experimental data. From these facts, we considered that the occurrences of high concentrations were captured by our LES model. From the above results, we considered that the basic performance of our LES model was almost comparable level to that

Here, we discuss the applicability of the present LES model for flow and dispersion around an isolated building to the problem of plume dispersion within a group of buildings. Within an urban canopy, three typical flow patterns, isolated flow, wake interference flow and skimming flow within building arrays are formed depending on the ratio of the buildings height to the street width and the flow filed is highly complex (Oke., 1998). Considering a surface geometry of urban canopy is composed of a group of isolated buildings and obstacles, numerical simulation with moderate grid points for each building and obstacle can capture such complex flow patterns with reasonable accuracy. Therefore, from the validation of our LES model for turbulent flow and plume dispersion around an isolated building, it is considered that the present model with moderate grid points for each building

Csanady, G.T. (1973). *Turbulent Diffusion in the Environment*, D.Reidel Publishing Co.,

**6. Conclusion** 

obstacles in the driver region.

**7. References** 

obtained by the wind tunnel experimental techniques.

Dordrecht, Holland, 222-248

can apply to a simulation of plume dispersion within urban canopy.


**16** 

*1India 2Singapore* 

R. C. Mehta1,2

*1Noorul Islam University, Kumaracoil,* 

*2Formally, Nanyang Technological University* 

**Computations of Flowfield over Reentry Modules at High Speed** 

A high-speed flow-past a reentry capsule generates a bow shock wave which causes a rather high surface pressure and as a result the development of high aerodynamic drag which is require for aero-braking purposes. Highly blunt configurations are generally preferred to decelerate space-capsule for safe returning on the Earth after performing the experiments. The bow shock wave is detached from the blunt fore-body and is having a mixed subsonicsupersonic region between them. The wall pressure distribution, the location of the sonic line and shock stand-off distance on the spherical cap region have been analytically calculated at very high speeds with an adiabatic index near to unity which gives a singular point at 60 deg from the stagnation point (Chester, 1956; Freeman 1956). The analytical approach for the high-speed flow over the blunt-body is considerably difficult and complex (Lighthill 1957). The flow-field over the reentry capsule becomes further complicated due to

Reentry capsule configurations significantly differ from each other due to entry conditions, trajectory, and a number of aerodynamic factors such as aerodynamic axial force, normal force, static moment, damping coefficients. This leads to the necessity to investigate the influence of the shape of blunted bodied on the flow field and aerodynamic characteristics. (Bedin et al., 1992) have presented aerodynamic characteristics and geometrical parameters for the sixteen different reentry modules using experimental data of ballistic test facility. Aero-assist flight experiment (AFE) configurations have been analyzed using two different Navier-Stokes flow solvers by (Venkatapathy et al., 1991). Aerodynamic heating and pressure along with the fore-body and wake-flow structure during atmospheric entry of the Mars Pathfinder spacecraft have been computed by (Hass & Venkatapathy, 1995) using the commercially available general atmospheric simulation program (GASP 2.2). An aerodynamic analysis of the commercial experiment transport (COMET) reentry capsule has been carried out by (Wood et al., 1996) solving the laminar thin layer Navier-Stokes LAURA code for low supersonic to hypersonic speeds. The LAURA code is an upwind, point implicit, second-order accurate fluid dynamics solver based on an extension of the Roe fluxdifference splitting scheme. (Yamomoto & Yoshioka, 1995) carried out flow field computation over the OREX (orbital reentry experiments) using computational fluid dynamics approach coupled with the thermal response of the heat shield material using

the presence of corner at the shoulder and the base shell of the reentry module.

**1. Introduction** 

