N. Yagnesh Sharma

CFD Analysis on the Effect of Radial Gap on Impeller-Diffuser Flow Interaction as well as on the Flow Characteristics of a Centrifugal Fan

The flow between the impeller exit and the diffuser entry (i.e., in the radial gap is generally considered to be complex). With the development of PIV and CFD tools such as moving mesh techniques, it is now possible to arrive at a prudent solution compatible with the physical nature of flow. In this work, numerical methodology involving moving mesh technique is used in predicting the real flow behavior, as exhibited when a target blade of the impeller is made to move past corresponding vane on the diffuser. Many research works have been undertaken using experimental and numerical methods on the impeller-diffuser interactive phenomenon. It is found from the literature that the effect of radial gap between impeller and diffuser on the interaction and on the performance of the fan has not been the focus of attention. Hence numerical analysis is undertaken in this work to explore and predict the flow behavior due to the radial gap. This has revealed the presence of an optimum radial gap which could provide better design characteristics or lower loss coefficient. It is found that there is a better energy conversion by the impeller and enhanced energy transformation by the diffuser, corresponding to optimum radial gap. The overall efficiency also found to increase for relatively larger gap.

CFD Simulation of Flow in an Abrasive Water Suspension Jet: The Effect of Inlet Operating Pressure and Volume Fraction on Skin Friction and Exit Kinetic Energy

Abrasive particles in the suspension mixture in an abrasive water suspension jet (AWSJ) machining causes acute skin friction effect thereby effectively changing the jet diameter due to wear, which in turn influences jet exit kinetic energy. This results in lowering the life of the jet for effective machining. In consideration of this aspect, the present work examines the effect of inlet pressure on skin friction coefficient and jet exit kinetic energy. It is inferred from the analysis that an increase in inlet pressure causes a significant increase in skin friction coefficient and also results in proportional increase in the exit kinetic energy of the jet. Further, it is revealed from the analysis that an increase volume fraction of abrasive (abrasive concentration) in water results in significant decrease in the skin friction coefficient and jet exit kinetic energy.

The effect of fuel volatility on droplet depletion rate and penetration of vaporizing fuel droplets in a Gas Turbine Combustor

It is well recognized that the fuel volatility has significant role in the dispersion and penetration of the fuel droplets sprayed into a combustor. Hence a study of the fuel droplet penetration and vaporization histories of a liquid fuel spray injected into a turbulent swirling flow of air through a typical can type Gas Turbine Combustor have been evaluated from numerical solutions of the conservation equations in gas and droplet phases. It is observed from the study that generally a higher swirl decrease the droplet penetration rate irrespective of the fuel volatility, but the effect is more pronounced for lighter droplet particles of n hexane than for the heavier kerosene droplets. Also an increase in spray cone angle shows a drastic reduction in the penetration of the spray. The effect of fuel volatility is marginal for different Spray cone angles as the droplet penetration is dictated more by the spray dynamics due to changed spray cone angle than the fuel volatility. But an increase in combustor pressure reduces the droplet penetration considerably. The fuel droplets with higher volatility seem to travel longer in a higher ambience more due to decreased rate of vaporization at higher pressure.

Numerical analysis of a centrifugal fan for performance enhancement using boundary layer fences on the volute casing

Flow within the centrifugal impeller and diffuser passage is a decelerating flow with an adverse pressure gradient along the stream wise path. This flow tends to be in a state of instability with flow separation zones. Several experimental attempts were made to assess the effectiveness of using boundary layer fences to realign the flow in the regions of flow separation to make the flow align itself into stream wise direction so as to minimize the loss and improve the overall efficiency of the diffusion process. With the development of CFD, a numerical whole field analysis of the effect of boundary layer fences in discrete regions of suspected separation points is possible. However it is found from the literature that there has been no significant attempt to use this tool to explore numerically, the utility of the fences on the flow field. This paper attempts to explore the effect of boundary layer fences corresponding to various geometrical configurations on the volute casing. It is shown from the analysis that the fences mounted on the initial half measured from the tongue of the volute casing surface improves the static pressure recovery across the fan. Fences provided elsewhere on the casing does not show any improvement in the performance of the fan.

Numerical analysis of a centrifugal fan for performance enhancement using boundary layer suction slots

Abstract Flow in centrifugal fans tends to be in a state of instability with flow separation zones on both the suction surface and the front shroud. The overall efficiency of the diffusion process in a centrifugal fan could be enhanced by judiciously introducing the boundary layer suction slots. With easy accessibility of computational fluid dynamics (CFD) as an analytical tool, an extensive numerical whole field analysis of the effect of boundary layer suction slots in discrete regions of suspected separation points is possible. This article attempts to explore the effect of boundary layer suction slots corresponding to various geometrical locations on the impeller as well as on the diffuser. The analysis shows that the suction slots located on the impeller blade near to its trailing edge appreciably improves the static pressure recovery across the fan. Slots provided at a radial distance of 30 per cent from the leading edge of the diffuser vane also significantly contribute to the static pressure recovery across the fan.Flow in centrifugal fans tends to be in a state of instability with flow separation zones on both the suction surface and the front shroud. The overall efficiency of the diffusion process in a centrifugal fan could be enhanced by judiciously introducing the boundary layer suction slots. With easy accessibility of computational fluid dynamics (CFD) as an analytical tool, an extensive numerical whole field analysis of the effect of boundary layer suction slots in discrete regions of suspected separation points is possible. This article attempts to explore the effect of boundary layer suction slots corresponding to various geometrical locations on the impeller as well as on the diffuser. The analysis shows that the suction slots located on the impeller blade near to its trailing edge appreciably improves the static pressure recovery across the fan. Slots provided at a radial distance of 30 per cent from the leading edge of the diffuser vane also significantly contribute to the static pressure recovery across the fan.