Abstract
Impeller trimming is a key impeller modification. It allows the best efficiency point (BEP) to be moved towards the region of lower flowrate and height, thus optimizing pump performance for specific piping systems. The paper deals with prediction of trimming results using CFD methods. Experience shows that modification of the BEP position depends on the trimming method as well as on the pump type and its specific speed. The analysed pump is of diagonal type with a specific speed of nb = 0.168. Its impeller is of a 4-blade design and a spiral casing is used as a volute. Seven cases of trimming are presented (including a non-trimmed original version). The paper compares CFD obtained data and data measured on an experimental stand. Additionally, the approach to CFD analysis, as well as the use of a turbulence model and characteristics of internal pump volume meshing are described.
Highlights
In order to keep manufacturing costs low, every pump manufacturer tries to cover the biggest possible region in a Q-Y (Flowrate-Specific energy) chart with a minimal number of manufactured pump types
The best efficiency point (BEP) point of each curve is the same as the point of maximum efficiency marked as ηmax, and it changes with each trimming stage
The key aspect is the determination of the BEP point position change represented by flowrate, specific energy and value of maximum efficiency achieved by computational fluid dynamics (CFD) simulation
Summary
In order to keep manufacturing costs low, every pump manufacturer tries to cover the biggest possible region in a Q-Y (Flowrate-Specific energy) chart with a minimal number of manufactured pump types. The simplest form of trimming is applied to pumps with a radial impeller as the trailing edge is located on a cylindrical surface. In such a case, the trimming results depend on a simple change of the impeller outer diameter D2. A significant tool contributing to make parameter change prediction of trimmed impellers more accurate is the method of computational fluid dynamics (CFD) simulation [1, 5] This method is helpful in the development of trimming stages as it allows the user to change all geometric parameters including trailing edge shape. Results obtained by the simulation are compared to the ones measured experimentally
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