SIMULATION OF HEAT TRANSFER FROM CANOPY SURFACES USING LOW-REYNOLDS NUMBER k-E MODEL

This study focuses on the Convective Heat Transfer Coefficient (CHTC) from urban building surfaces by numerical simulation. The heat transfer effects because of various geometrical and physical properties of urban areas exhibits a differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI) phenomena. Investigation of Convective heat transfer coefficient becomes more important in the study of urban heat island phenomena. Experimental simulation of urban area with various urban canopy cases in thermally stratified wind tunnel is employed for the heat transfer kind of investigations in urban area. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces transfer such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, Water evaporation technique used in wind tunnel experiment for the evaluation of convective heat transfer coefficient and naphthalene sublimation technique conducted by other researchers are used to validate the low-Reynolds-number k-ε model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with both water evaporation technique and naphthalene sublimation experimental results. It is found that the low-Reynolds-number k-ε model is reliable for the investigations pertaining to heat transfer from urban canopy

FLOW VELOCITY AND SURFACE TEMPERATURE EFFECTS ON CONVECTIVE HEAT TRANSFER COEFFICIENT FROM URBAN CANOPY SURFACES BY NUMERICAL SIMULATION

This study investigates the effect of flow velocity and building surface temperature effects on Convective Heat Transfer Coefficient (CHTC) from urban building surfaces by numerical simulation. The thermal effects produced by geometrical and physical properties of urban areas generate a relatively differential heating and uncomfortable environment compared to rural regions called as Urban Heat Island (UHI) phenomena. The urban thermal comfort is directly related to the CHTC from the urban canopy surfaces. This CHTC from urban canopy surfaces expected to depend upon the wind velocity flowing over the urban canopy surfaces, urban canopy configurations, building surface temperature etc. But the most influential parameter on CHTC has not been clarified yet. Urban canopy type experiments in thermally stratified wind tunnel have normally been used to study the heat transfer issues. But, it is not an easy task in wind tunnel experiments to evaluate local CHTC, which vary on individual canyon surfaces such as building roof, walls and ground. Numerical simulation validated by wind tunnel experiments can be an alternative for the prediction of CHTC from building surfaces in an urban area. In our study, wind tunnel experiments were conducted to validate the low-Reynolds-number k-ε model which was used for the evaluation of CHTC from surfaces. The calculated CFD results showed good agreement with experimental results. After this validation, the effects of flow velocity and building surface temperature effects on CHTC from urban building surfaces were investigated. It has been found that the change in velocity remarkably affects the CHTC from urban canopy surfaces and change in surface temperature has almost no effect over the CHTC from urban canopy surfaces

Structural features of eggs of the basal phasmatodean Timema monikensis Vickery & Sandoval, 1998 (Insecta: Phasmatodea: Timematidae)

Structural features of the eggs of a basal phasmatodean, Timema monikensis Vickery & Sandoval, 1998 (Timematidae) were examined. The eggs of this species are soft and deposited coated with soil and/or other extraneous particles. The chorion, which is transparent and weakly sclerotized, is composed of an endochorion and an exochorion. The non-inclined operculum is located at the anterior pole of the egg. The chorion in the marginal region of the operculum is thinned to form an opercular collar together with the chorion of the egg body. An inverted triangular micropylar plate is on the ventral side of the egg attached to the opercular collar. The micropylar plate is without external differentiations but is specialized inside the chorion. A single micropyle, with a simple funnel-shaped chorionic opening, occurs on either side of the micropylar plate. The posterior mound, located at the posterior pole, is a thickened chorion rich in fine vertical striations, and the serosal cuticle beneath is thickened and highly specialized. The eggs of Timematidae were characterized and compared with those of Euphasmatodea and Embioptera. A phylogenetic discussion is presented, strongly supporting the assemblage of Timematodea, Euphasmatodea and Embioptera as monophyletic

Pedestrian wind environment around tall buildings

Pedestrian-level wind conditions around tall buildings are described by examining the aerodynamics of the urban environment and the various wind comfort criteria established in the wind engineering field. Experimental and, possibly, computational assessment of pedestrian-level wind conditions in the urban environment are described in detail. Particular emphasis has been placed on the state of the art and the capabilities of Computational Wind Engineering to determine at least mean values of wind speeds in the vicinity of buildings in urban areas. An approach toward the establishment of an overall comfort index taking into account, in addition to wind speed, the temperature, and relative humidity in the urban area under consideration, is presented

Experimental and Numerical Study on Natural Convection in a Model Fire Room

本研究は火災時の煙流動のように密度変化が大きく, 流体の非圧縮性を仮定することの難しい大きな温度差のある流れ場をCFDにより解析し, 実験との比較によりその妥当性を検証することを目的とする. 本報では, モデル火災室内の高温自然対流をLDV等を用いて詳細に測定した結果と, 浮力ダンピング効果を考慮した低Re数型圧縮性k-εモデルによる3次元乱流数値シミュレーション結果を比較検討する.特集 乱流の数値シミュレーション(NST)その1