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ABSTRACT
Pre-swirl occurring in pump intake basins influences pump efficiency and lifetime. The exact effect on a pump depends on the pump design. In order to optimize the approach flow towards the pump, physical scale modelling is often applied following the guidelines formulated in pump intake design standard ANSI/HI 9.8-2012. This standard provides guidelines on measurement equipment for, and acceptance criteria of, swirl. As this standard does not elaborate on the measurement technique, an approach is proposed through which a swirl can be quantified with a known accuracy in a sump model test. The proposed method is demonstrated using two scale models where swirl was measured for 6 hours. Furthermore, conditions where the acceptance criteria of ANSI/HI 9.8-2012 are not strictly defined are outlined and quantifiable acceptance criteria for future sump model tests proposed.
Notation
| cn | = | absolute velocity at location n (m s–1) |
| Di | = | internal diameter of the suction tube (m) |
| i | = | detector index (–) |
| nd | = | number of detectors (–) |
| nm | = | number of magnets (–) |
| nCW | = | number of clockwise revolutions of the propeller in a specific time span (rpm) |
| nCCW | = | number of counter-clockwise revolutions of the propeller in a specific time span (rpm) |
| Q | = | the total flow rate through the suction line (m3 s–1) |
| r | = | radius of suction line (m) |
| rswirl | = | resolution of measurement (°) |
| Δt | = | measurement time (s) |
| un | = | peripheral velocity at location n (i.e. blade velocity) (m s–1) |
| vt | = | tangential velocity of the swirl meter (m s–1) |
| va | = | axial flow velocity in the suction tube (m s–1) |
| wn | = | relative velocity at location n (m s–1) |
| xi | = | parameters that influence the measurement error (–) |
| α | = | angle between detectors (°) |
| βn | = | minimum angle before detector encounters a magnet (°) |
| γn | = | local impeller blade angle at location n (°) |
| = | sum of rotation since start of measurement (rad) | |
| ω | = | angular velocity (rad s–1) |
| σ | = | standard deviation (%) |
| θ | = | swirl angle (°) |