Influence of low-specific speed pump modifications on stability of Y-Q curve

Abstract

Abstract. Contribution is focused on modification of low-specific speed pump impellers with respect to stability of their Y-Q curves (i.e. head curves). The design modifications are driven by analysis of the dissipated power. First, dissipated power is evaluated by CFD software in individual working parts of the pump and then its dependence on flow rate is investigated. Pressure fields within the pump are also carefully examined. Special attention is paid to impellers and configuration of the blade channels and recirculating channels. Results point to significant influence of the proper inflow to recirculating channels and also to role of the volute, which is more pronounced than in conventional impellers. All integral characteristics from CFD simulations are verified experimentally.

Influence of recirculation on Y-Q characteristic curve of hydrodynamic pump

“…dissipation) and could not be verified by appropriate experiments, was authenticated primarily by using integral characterictics like hydraulic efficiency and specific energy curves. There is correspondence between experimental data and data obtained from CFD in case of spiral case S1 [5]. In case of impeller with thick trailing edges with Lshaped recirculation channels there could possibly appear a moderate instability in the area of shut-off point.…”

“…There is one interesting fact connected with the curve of specific energy of the impeller with L-shaped recirculation channels. There can be seen some shift of this curve, which causes the curve of specific energy to appear more stable than it was shown in case of spiral case S1 [5]. Values of hydraulic efficiency remained preserved in the design point.…”

“…The flow areas in individual sections of the spiral case were preserved. The spiral case S1 was in fact designed for specific assembly conditions of the pump [5].…”

“…Unfavorable fact is that the magnitude of the rate-ofstrain tensor vij could not be determined precisely enough through CFD simulations, see [5]. Therefore, it is appropriate to use the difference of input and output powers instead to determine the magnitude of the dissipated power.…”

“…The contribution of aforementioned regions to stability of specific energy curves will be assessed afterwards, at first the curves of dissipated power will be analyzed. The reasons for modifications of the spiral case S1 to the spiral case S2 (see Figure 2) can be found in [5].…”