Simulation and Modeling of Ported Shroud Effects on Radial Compressor Stage Stability Limits

Abstract

The design features of a centrifugal compressor must guarantee high performance and a wide operating range. The ported shroud was developed specifically to extend the operating limit. It is a passive flow control device based on a cavity for flow recirculation to avoid blade passage blocking in near surge conditions. A CFD simulation campaign using a simplified model identified the differences in the performance of the centrifugal compressor with ported shroud, compared to the baseline case. The use of a stability criterion to determine the limit mass flow rate, developed in a previous study by the authors, highlighted and quantified the extension of the surge margin in the case with ported shroud for different rotational speeds. An increase in the surge margin of 11% was detected at design speed, but with a lower trend at higher speeds. An in-depth flow analysis showed the main physical mechanisms in the compressor that occur for different operating conditions: at near surge conditions the cavity recirculates the low momentum flow located in the inducer region; it re-energizes the mainstream decreasing the circumferential velocity component; an improvement of up to 7% of the pressure ratio was obtained. Instead, at best efficiency conditions the flow recirculation worsens the performance by reducing the flow incidence at the rotor leading edge. Finally, using unsteady simulations with a complete 3D model and with the application of the stability criterion it was possible to confirm that the ported shroud can effectively extend the operating range.

Early surge detection on a turbocharger used to pressurize a SOFC plant emulator

“…In the literature there are numerous theoretical studies and experimental investigations about surge inception where the aim is to allow full control of compressor behavior in the low flow range; indeed, the ultimate goal is to obtain a wider compressor functionality to supply boost pressure at all the required operating conditions [1][2][3][4][5]. Experimental investigations about compressor performance together with analysis of its vibro-acoustic behavior provide useful diagnostic insights; indeed, they enable a reliable early detection of low mass flow rate instabilities [6][7][8][9][10].…”

Numerical Evaluation in a Scaled Rotor-Less Nozzle Vaned Radial Turbine Model under Variable Geometry Conditions

“…For this reason, the stator can have, in some turbines, movable vanes that control and adapt the flow depending on the operating conditions. These variable geometry nozzles in the stator help to extend the operating range of the turbine; meanwhile, the matching with the compressor side can be achieved by the use of a ported shroud [21]. Uniform distribution over the 360 degrees of the radial stator is important to then adapt the flow at the rotor inlet, a matter of interest in [22], where they tested flow behavior for twin-entry turbines as two separated single VGT volutes.…”

A Computational Method of Rotating Stall and Surge Transients in Axial Compressor

“…Numerous solutions have been investigated to suppress the occurrence of compressor stall and to increase surge margin. Such as axisymmetric arc-shaped slots casing treatment investigated by Pan et al [1], the ported shroud was developed by Cravero et al [2] and radial injectors were tested by Khaleghi [3].…”