Estimation of shock loss factors at shaft bottom junction using computational fluid dynamics and scale model studies

CIM Journal, Vol. 1, No. 2, 2010
T. Purushotham, University of Alaska, Fairbanks, Alaska, B. S. Sastry and B. Samanta, Indian Institute of Technology, Kharagpur, India
Abstract

The shaft bottom junction in a mine ventilation system is an important source of shock loss due to the combined effect of bend and area change. The occurrence of high-volume flow rates through this configuration can potentially result in high energy losses. The current research examines the process of shock loss at a characteristic shaft bottom junction of an underground coal mine. Investigations are performed on both laboratory-scale models and three-dimensional computational fluid dynamics (CFD) simulations, under both exhausting and forcing shaft bottom conditions. The effects of the plat roughness and the shaft bottom length on the shock loss factor values are also examined. The studies show that the combined effect of bend and area changes that occur at the shaft bottom junction results in shock loss factors that are much higher than those values resulting from abrupt area change only. The transition from a smooth wall condition to an unlined rough airway condition (relative roughness, e/d = 0.112) can increase the shock loss factors by 40%. The effect of shaft bottom length on the shock loss factor has not been clearly established due to conflicting results produced by scale model studies and the CFD simulations.


Dans un système de ventilation minière, le raccordement dans le bas du puits constitue une importante source de perte par choc en raison de l’effet combiné d’un coude et d’un changement de section. La présence de taux élevés d’écoulement de grands volumes d’air dans une telle configuration peut potentiellement conduire à de grandes pertes d’énergie. La présente recherche étudie le processus de perte par choc à un raccordement typique au fond d’un puits dans une mine souterraine de charbon. Des essais sont effectués sur des modèles à l’échelle du laboratoire et sur des simulations tridimensionnelles par dynamique des fluides numérique (CFD) sous des conditions d’évacuation et de forçage d’air au fond du puits. Les effets de la rugosité de la plaque et la longueur au fond du puits sur les valeurs du facteur de perte par choc ont été examinés. Les études montrent que l’effet combiné d’un coude et d’un changement de section dans un raccordement au fonds du puits donne des facteurs de perte par choc qui sont beaucoup plus élevés que les valeurs résultant uniquement d’un changement abrupt de section. La transition d’une paroi lisse à une paroi rugueuse d’une conduite sans revêtement (rugosité relative e/d = 0,112) peut augmenter les facteurs de perte par choc de 40 %. L’effet de la longueur au fond du puits sur le facteur de perte par choc n’a pas été clairement établi en raison des résultats contradictoires des études sur modèle à l’échelle et des simulations CFD.
Keywords: k-? turbulence model, Forcing and exhausting ventilation shafts, Relative roughness, Shaft bottom length, Geometric and dynamic similitude, Modèle de turbulence, Puits d’évacuation et de forçage de la ventilation, Rugosité relative, Longueur au fond du puits, Similitude géométrique et dynamique
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