A CFD and experimental study on cavitation in positive displacement pumps: Benefits and drawbacks of the ‘full’ cavitation model

Figures & data

Figure 1. Test-rig schematic.

Note: The pumping system is shown but the pressure sensors on the pump are not shown.

Figure 2. Section of the PD pump on the symmetry plane.

Note: The chamber and valve-seat pressure sensor locations are shown (top and bottom detailed view, respectively) and the inspection window on the right of the bottom (suction) valve is shown.

Table 1. Pressure sensor characteristics summary.

Pressure sensor	Range (bar)	Absolute/ Relative	Maximum non-linearity [%]	Response time [ms]
Venturi Upstream	0–2.5	A
Venturi downstream	0–2.5	A
Chamber pressure	0–10	R
Valve-seat pressure	0–10	A	0.25	<0.5
Pressure outlet	0–6	A
Tank inlet	0–0.25	R
Tank outlet	0–0.25	R

Figure 3. Plunger displacements and velocities fed into the motor drive administration software are shown.

Figure 4. Decomposition pattern of the fluid volumes of the pump chamber (Iannetti et al., 2014a).

Note: The numbered items are listed in Table 3.

Figure 5. View of the mesh utilized for the analysis.

Note: The detailed section of the mesh is taken from the valve vicinity.

Table 2. Mesh sensitivity analysis for three mesh sizes.

Mesh	Number of cells (M)	Average skewness (-)	Approx. computational time (h)
1	3	0.24	48
2	5	0.26	60
3	6	0.22	72

Table 3. Mesh 2 details summary.

Location (see figure 4)	Volume description	Mesh type	Size details min–max [mm]	Mesh motion
1	Valve-seat lift	Hexahedral	0.2–1	Expanding
2	Inlet valve	Wedge	1–3	Compressing
3	Inlet valve	Hexahedral	2–3	Expanding
4	Displacement	Hexahedral	2.5–2.5	Expanding
5	Pump chamber	Tetrahedral	2.5–5	Static
6	Valve internal	Tetrahedral	1–2.5	Translating
7	Inlet manifold	Tetrahedral	2–4	Static
8	Valve top volume	tetrahedral	1–2	Translating

Figure 6. UDF scheme operations (Iannetti et al., 2014b).

Table 4. Solver settings summary.

Figure 7. (a) Pump chamber static pressure and (b) valve-seat static pressure for the experimental and CFD model results of Test 1.

Note: The CFD model was run with 3 ppm air content in the water.

Figure 8. (a) Second phase fraction composition according to the CFD model and (b) valve lift for the experimental and CFD model results of Test 1.

Note: The CFD model was run with 3 ppm air content in the water.

Figure 9. Null/incipient cavitation.

Note: Only three frames show vapor which does not obscure the view of the valve.

Figure 10. (a) Pump chamber static pressure (log scale) and (b) valve-seat static pressure (log scale) for the experimental and CFD model results of Test 2.

Note: The CFD model was run with 3 ppm air content in the water.

Figure 11. (a) Second phase fraction composition according to the CFD model and (b) valve lift for the experimental and CFD model results of Test 2.

Note: The CFD model was run with 3 ppm air content in the water.

Figure 12. Partial cavitation.

Note: Four frames show a vapor cloud around the valve-lift gap; in two of them, the view of the valve is obscured almost completely.

Figure 13. (a) Pump chamber static pressure and (b) valve-seat static pressure for the experimental and CFD model results of Test 3 demonstrating the sensitivity of the CFD model to the air mass fraction.

Figure 14. (a) The vapor volume fraction in the valve-seat lift volume and (b) the air volume fraction in the valve-seat lift volume according to the CFD model of Test 3.

Figure 15. Valve lift for the experimental and CFD model results of Test 3 demonstrating the sensitivity of the CFD model to the air mass fraction.

Figure 16. Full cavitation.

Note: Five frames show a vapor cloud around the valve-lift gap; in four of them, the view of the valve is completely obscured.

Figure 17. FFT of the chamber pressure signals for the experimental and CFD model results of Test 3.

Iannetti, A., Stickland, M. T., & Dempster, W. M. (2014a). An advanced CFD model to study the effect of non-condensable gas on cavitation in positive displacement pumps. In 11th international symposium on compressor & turbine flow systems theory & application areas SYMKOM 2014 IMP2. Lodz, Poland.

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Iannetti, A., Stickland, M. T., & Dempster, W. M. (2014b). A computational fluid dynamics model to evaluate the inlet stroke performance of a positive displacement reciprocating plunger pump. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 228(5), 574–584.

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