Effect of adding short blades on centrifugal pump performance and dynamic stability

الملخص EN

Centrifugal pumps are used extensively for hydraulic transportation of liquids over short to medium distance through pipelines where the requirements of head and discharge are moderate.

The improvement of centrifugal pumps characteristics is important reduce the consumption of energy.

One possible modification is to break down the circulation near the impeller exit using shorted blades.

Numerical simulation and experimental verification are used to investigate the effects of short baled geometry on flow field and dynamic analysis of centrifugal pump.

The model pump has a design specific speed of 23.75 rpm and an impeller with 7 blades.

The short blade length factor Lb ratio varied from 0.16, 0.25 and 0.3 respectively from the impeller blade length.

Other geometric parameters are kept constant.

The inner flow fields and characteristics of the centrifugal pumps with different short blade lengths are simulated and predicted using commercial code Fluent under Ansys Ver.14.5.

A test rig for testing centrifugal pump with standard impeller and three impellers of different shorted blade sizes is constructed.

The head, flow rate and shaft power are evaluated for each pump configuration to show the effect of these shorted blades sizes on pump performance.

When add short blades, with length ratio Lb = 0.25, the vibration level increased to reach 1.32 mm/s.

A 30 % increase in vibration level is found compared to impeller without short blades; whoever, vibration level is still within the allowable level according to the international standards (ISO 10816-3).

High frequency analysis shows that, the bearing is affected by adding short blades.

For impeller with additional short blades between the main blades, H increased by 3.78 m (11.68 %), and η by (6.95 %).

The power consumption in the case of blade length ratio Lb = 0.25 approximately constant compared with the total energy consumption without impeller short blades with no power saving.

Time averaged numerical results are compared with the experimental performance curve and good agreement has been achieved.