Research on Performance of Large Vertical Medium and Low Specific Speed Fixed Guide Vane Centrifugal Pump
The cooperation of guide vane, impeller and volute affects the flow in the pump
-Mismatched guide vanes will cause the following phenomena
-Deflow from the blade inlet
-Secondary flow in the runner
-Large pressure pulsation and noise
-Partial cavitation
The above unsteady flow adversely affects the performance of the pump.
Simulation pump size
-Similar to the prototype pump
-Spiral water chamber with fixed guide vanes
Simulation test system
-Universal test bench for hydraulic machinery model
-The comprehensive error of the model efficiency experiment is less than 0.2%
-Closed cycle test system
Test Method
-Guide vanes with different placement angles and lengths were used in the test
-Guide vane for the first and second cut
• The inflow angle% was adjusted to 15, 11, and 9.5, respectively.
Model tests of centrifugal pump efficiency, cavitation, pressure pulsation, etc. are based on
IEC 60193: 1999 standard at 1200rpm
Three-dimensional numerical simulation (prototype pump)
-Hexahedral structured grid with a total of 4.75 million elements and 4.7 million nodes
One Ansys CFX 10.0
-Turbulence model: RNG k- £
One Inerface: Frozen rotor
-Rotation speed: 600 rpm
-Boundary conditions:
• Import: static pressure
• Outlet: mass flow
• Side wall: no-slip
Simulation test results
Centrifugal pump characteristics
-ψ is between 0.63 and 1.12. As Φ decreases, the design condition (Φ = 0.10) ψ is about 0.96.
-The same guide vane angle (15 ° or 9.5 °):
• Different guide vane lengths have similar ψ characteristics.
-The same guide vane length (SV1):
• Different guide vane placement angles (15 °, 11 ° or 9.5 °), ψ characteristics vary greatly.
Centrifugal pump performance: efficiency curve
-The optimal efficiency points of different models are all near the design operating point (Φ = 0.101), but the opening of the large guide vane is most advantageous in the direction of large flow. The highest prototype efficiency ηp obtained in the experiment was 89.83%.
-β3 = 9.5 ° model
• With higher optimal efficiency, it shows that the guide vane and impeller are more reasonable.
-Large guide vane placement angle model
• Has a wider area of high efficiency
(Φ = 0.098-0.15)
• The highest efficiency moves to the direction of large flow.
Cavitation performance (plant condition of NPSHp = 56.6 m for SV1 model at β3 = 9.5 °)
-In the range of Φ <0.098, cavitation has no obvious effect on the characteristics of the pump, because under this condition, although cavitation has occurred, the performance of the pump will only deteriorate when the NPSH drops to a very low level.
Numerical simulation results
-The errors of the heads are
1.05%, 1.60% and 3.87%, which is in good agreement with the test.
-The loss in the guide vane accounts for more than 80% of the loss in the pump, and the volute accounts for about 6 ~ 8%. Therefore, the guide vane is the main over-current component of the loss in the pump.
The internal flow of the centrifugal pump at the design working point
-Near the interface of impeller and guide vane:
• Irregular flow
• Uneven pressure distribution
-Flow shock at the inlet of the guide vane
-2 vortices appeared in the flow channel
• Flow path between blades N0.13 and N0.1
• Flow path between blades N0.2 and N0.3
Conclusion
• The matching of guide vane and impeller affects the performance of the centrifugal pump. The guide vane placement angle has a significant effect on the head and efficiency of the centrifugal pump.
• The dynamic and static interference of the impeller and guide vane causes a large pressure pulsation at the impeller-free area of the impeller outlet.
• The flow pattern at the inlet of the guide vane is turbulent, causing the main loss of the centrifugal pump in the guide vane area, accounting for more than 80% of the hydraulic loss.
