Design and Testing of Multistage Centrifugal Compressors With Small Diffusion Ratios

Abstract

Two stators of a multistage centrifugal compressor with progressively smaller outer radii have been designed, built, and tested. The aim was to achieve a significant reduction in the outer diameter of the compressor stage without compromising performance. The reduction in size was achieved by reducing the diffusion ratio (outer radius/inner radius) of the vaneless diffuser in two steps. In the first step, the outer diameter of the entire stage was reduced by 8% compared with the baseline design. In the second stage, the outer diameter was reduced by 14%. The outer radius of the smallest design was limited by the impeller exit diameter, which was kept constant, as was the axial length of the stage. The large radius baseline design has been tested on a rotating rig in a 1.5 stage setup. This setup aimed at simulating the multistage behavior by applying a pseudostage upstream of the main stage. The pseudostage consisted of a set of nonrotating preswirl vanes in order to mimic an upstream impeller and was followed by a scaled version of the return channel of the main stage. The experimental database was then used to calibrate a 1D analysis code and 3D–computational fluid dynamics methods for the ensuing design and optimization part. By applying an extensive design-of-experiments, the endwalls as well as the vanes of the stator part were optimized for maximum efficiency and operation range. In order to preserve the multistage performance, the optimization was constrained by keeping the circumferentially averaged spanwise flow profiles at the exit of the smaller radius stages within close limits to the original design. The reduced radius designs were then tested in the same 1.5 stage setup as the baseline design. The results indicate that the reduction in size was feasible without compromising the efficiency and operation range of the stage.

The Design of a Family of Process Compressor Stages

“…The recent work of Aalburg (2008) which suggests that a radius ratio of 1.3 is possible with no loss in performance is not considered to be appropriate. The return channel components have a relatively high loss coefficient (with a typical value of 0.4) and it is important to reduce the kinetic energy at inlet to the crossover bend to avoid large losses in these components.…”

Cavity Flow Modeling in an Industrial Centrifugal Compressor Stage at Design and Off-Design Conditions

“…Previous validations and modeling experiences with TACOMA on centrifugal compressor stages can be found in [16], [17], [18] , [1] and [19] .…”

“…5 showing the very good grid details including a correct boundary layer grid clustering. The grid size was based on GE internal best practices and past validations (see also [1], [16], [17] and [18].) Also a grid sensitivity analysis has been done on this test case.…”

Deficits in Rans Modelling in the U-Turn of a Multistage Centrifugal Compressor

“…His findings support Rothstein`s conclusions. Recent publications by Aalburg et al [3] and Rossbach ([4], [5]) focus on detailed flow phenomena with the aim of reducing the diffuser radius ratio, in turn motivated by the manufacturer need to reduce CAPEX by reducing machine size. However, with a lower diffuser ratio, the flow velocity inside the return bend and the return guide vanes (RGV) increases, promoting secondary flows and thus increased turbulence intensity due to higher shear rates.…”