Optimized Valve Design to Reduce Cavitation

Optimized Valve Design to Reduce Cavitation

                                                                                                              Project Aims

The main aim of this project is to develop an improved understanding of the cavitation process which may occur within the inlet valve, valve seat and pump chamber of an SPM positive displacement pump through simulation of the pumping cycle using computational fluid dynamics (CFD). Cavitation bubble collapse may result in localized pitting which causes erosion, stress concentration and corrosion damage reducing the pump life. A better understanding of cavitation  means improving pump design and life.

 

CFD Model

CFD Model Achievements

 

1.Transient  Euler first order implicit simulations, 2 operative conditions results presented: 1 and 2 bar inlet manifold pressure cases.
2.Turbulent flow, k-epsilon coupled with enhanced wall treatment
3.Compressible fluid via User Defined Function
4.Two phase model (water + vapour) with non-condensable gases effect
5.Singhal Et Al.  cavitation model
6.Second order upwind discretization schemes for mixture velocity, k, epsilon
.

Case 1: Inlet pressure 2 bar, incipient cavitation conditions. Depending on the operative conditions, valve mass, spring preload and stiffness, the minimum pressure barely touches the vapour pressure value for the room temperature (3000 Pa), non-condensable gases expand while the pressure decreases and a negligible quantity of vapour is produced (the sequence on the left). The valve lift history closely follows the plunger displacement history with a small delay due to its inertia and to the spring preload, the mass flow history closely follows the theory

Case 2: Inlet pressure 1 bar, developed cavitation conditions. Decreasing the inlet manifold pressure at 1 bar (room condition) the chamber pressure reaches the vapour pressure value and remains enough to create a high quantity of vapour (up to 100 % in volume fraction, sequence on the left)  non-condensable gases expand but insufficiently to stop the vapour production. The valve lift history does not follow the plunger displacement anymore and experiences a remarkable delay due to the time needed to destroy the vapour at the end of the stroke (graphs below).

 

Future Improvements

Experimental tests are being designed to validate CFD models. After validation, CFD technique discussed will be considered ready to be applied for:
  • Investigating separately each parameter affecting valve dynamics and, therefore, cavitation.
  • Design and optimize new valves

For more information about the project contact Dr Matt Stickland (matt.stickland@strath.ac.uk), Senior Lecturer at Department of Mechanical and Aerospace Engineering, University of Strathclyde.
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