Punit Singh

EXPERIMENTAL AND COMPUTATIONAL STUDIES OF THE EFFECT OF 'CASING EYE RIB' ON THE SWIRL FLOW AT THE EXIT OF A PUMP AS TURBINE

This paper presents a detailed hydraulic analysis of the effects of the casing eye rib on a pump operating as a turbine. It describes a flow-zone approach within a pump as turbine and lays out the build up for the experimental and numerical techniques applied. The pump as turbine exhibits very good characteristics with a maximum operating efficiency over 82%. The similitude between experimental and numerical results has been satisfactory. The two stages namely the ‘casing rib present’ and the ‘casing rib absent’ stage are compared at 6 different load points encompassing the entire characteristics. Both methods reveal that the performance of the PAT has enhanced without the presence of the rib. However the two methods show different causes for this behaviour. The comparison of the swirl profiles reveal that the fluid in the ‘casing rib absent’ stage has greater rotational momentum in the part-load and overload region compared to the ‘casing rib present’ stage. However the ‘casing rib absent stage’ displays more symmetric swirl profiles. At the end of the paper, an uncertainly analysis for the experimental efficiency is carried out.Copyright

Influence of the Blade Hub Geometry on the Performance of Low-Head Axial Flow Turbines

AbstractThe influence of geometric parameters, such as blade profile and hub geometry on axial flow turbines for micro hydro application remains poorly characterized. This paper first introduces a holistic theoretical model for studying the hydraulic phenomenon resulting from geometric modification to the blades. It then describes modification carried out on two runner stages, of which one has untwisted blades and the other has twisted blades obtained by modifying the inlet hub. The experimental results showed that the performance of the untwisted blade runner was satisfactory with a maximum efficiency of 68%. However, positive effects of twisted blades were clearly evident with an efficiency rise of more than 2%. This study also looks into the possible limitations of the model and suggests the extension of the experimental work and the use of computational tools to conduct a progressive validation of all experimental findings, especially on the flow physics within the hub region and the slip phenomena. T...

Impeller performanceAxial flow impeller shapes: part 2

In this second of two articles concerning axial flow impellers, Punit Singh and Franz Nestmann of Karlsruhe Institute of Technology focus on backward curved impellers, revealing hydraulic behaviour that is interesting and unexpected in pump and turbine operations respectively. They also compare the performance of forward and backward curved impellers to determine the optimum impeller shape for turbines. The background and objectives of this two-part series were discussed in detail in the previous article 1 . As mentioned, this second article will closely analyse the performance of backward curved axial flow impellers for both pump and turbine operations, as well as covering the remaining objectives of the study, namely: a) To apply the theoretical model (developed in part 1) to backward curved impellers and look at nuances within the internal hydraulics in both pump and turbine operations. b) To search for the optimum turbine impeller after comparing the turbine operations of forward and backward curved impellers. c) To establish steps for modelling the four-quadrant characteristics of pumps with both forward and backward curved impellers.