A First Analysis of Flow Field Hysteresis in a Pump Impeller

Abstract

The measured pump pressure discharge characteristic for a high specific speed radial pump (ωs = 1.7) reveals distinct discontinuities in part load operation. These pressure discontinuities occur at different threshold volume fluxes when increasing or decreasing the pump discharge and make up a hysteresis loop. The pump impeller characteristic was evaluated experimentally and numerically by taking the difference between the integrated impeller outlet and impeller inlet total pressure. The experimental and numerical characteristics agree well including the volume flux location and magnitude of the pressure discontinuities in the hysteresis loop. For volume fluxes within the hysteresis loop two stable well converged flows were calculated numerically. The numerical calculations were made on coarse and fine grids using commercially available software with and without the impeller clearance leakage flow. Further experimental and numerical comparisons are made at the impeller inlet/outlet with emphasis on the changing flow field in the hysteresis loop flow regime and its coupling to the onset of reverse flow zones. This combined application of numerical and experimental tools provides insight for the hysteresis flow field of a pump impeller characteristic.

Large-eddy simulations in mixed-flow pumps using an immersed-boundary method

“…They also investigated the sensitivity of these patterns to the tip-clearance. Kaupert et al [13] investigated the effects of pressure discontinuities in high-specific-speed radial pumps, showing reasonable agreement between experiments and computations. More recent RANS applications include the study of the flow in a backswept centrifugal impeller by Zhang and coworkers [32,33], the impeller-diffuser interaction in a diffuser pump stage [20] and various configurations in turbopumps [9,3].…”

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

“…For the experimental method, Equation (4) gives an approximate value of Euler torque [16]. Energy coefficients for hydraulic losses and gross energy obtained from the rotating runner could be calculated through the Equations (6) and (7). Number (3) already used -renumber equations…”

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

“…However, it has rarely been observed in hydraulic machinery. It is firstly described in 1997 by Kaupert and Staubli [7] referring to a high specific speed (ω s = 1.7 s´1) radial pump. When measured in two directions (decreasing or increasing discharge), performance characteristic (H-Q) appears different in the hump region.…”