Frictional Effects on a Base and a Flow-Trimmed Impeller of a Low Specific Speed Industrial Compressor

Abstract

Flow-trimming base designs for lower flow applications are widely used in the turbo-machinery industry to minimize development costs. This process requires the use of the same casing as the base design, along with a decrease in the flow path width of the impeller, diffuser, crossover, and return vane. Two stages: a baseline and a flow-trimmed impeller, diffuser and return vane are studied in this paper to review impacts on performance and their underlying causes. To measure the performance changes of the two rigs, a traverse survey for flow angle and total pressure was done at the locations of diffuser inlet, return vane leading edge and stage discharge. It was found that the performance difference between the base impeller and trimmed one is very little. However, diffuser performance of the base rig is better than the flow-trimmed rig. Diffuser data shows frictional losses increased in the flow-trimmed rig. Rig data also suggests that increased friction in the trimmed stage changes the flow angle at the return vane leading edge compared to the base stage. This increases the loss further for the flow-trimmed rig because of resulting negative incidence on the return vane relative to the base rig. Data suggests that while flow-trimming may be a valid design approach for impellers, additional issues arise when downstream stationary components are trimmed.

Effect of impeller blade trimming on the performance of a 5.5:1 pressure ratio centrifugal compressor

“…A study by David et al. 2 found little difference in impeller efficiency between a baseline impeller and one trimmed for 75% of the baseline flow. Zhang et al.…”

“…Even though it is a common industrial practice to trim impeller blades, a scarcity of published literature has been noted by Rodgers 1 and David et al. 2 —two of the few works which directly address the topic.…”

Numerical study and experimental validation of the performance of two different volutes with the same compressor impeller

“…Based on references [8] and [9], it was reported that the maximum uncertainty of head from the test is +0.21 to −0.42 per cent and the uncertainty of efficiency is +0.23 to −0.45 per cent. As the test accuracy is pretty good, the small uncertainties will not be plotted in the figures.…”

Influences of the Flow Cut and Axial Lift of the Impeller on the Aerodynamic Performance of a Transonic Centrifugal Compressor

“…Rogers recommended that the flow cut method should be applied only at a nondimensional specific speed (Ns) between 0.5 and 1.2. Tim David (2006) and Donghui Zhang (2010) applied the flow cut method by up to 75% (a flow fraction of 0.25 compared to the design flow rate of the base compressor) to the impeller of an industrial compressor with a nondimensional specific speed (Ns) of 0.06. However, Tim David and Donghui Zhang recommended applying only 50% of the flow cut to the impeller [11,12].…”

“…Tim David (2006) and Donghui Zhang (2010) applied the flow cut method by up to 75% (a flow fraction of 0.25 compared to the design flow rate of the base compressor) to the impeller of an industrial compressor with a nondimensional specific speed (Ns) of 0.06. However, Tim David and Donghui Zhang recommended applying only 50% of the flow cut to the impeller [11,12]. Daniel applied the flow cut and axial trim methods to different types of impellers such as a transonic impeller with a relative Mach number between 0.8 and 1.2 at the impeller inlet tip, a closed impeller without tip clearance, and an impeller without a splitter [13].…”