Ismail Hakki Sezal

INTRODUCTION OF CIRCUMFERENTIALLY NON-UNIFORM VARIABLE GUIDE VANES IN THE INLET PLENUM OF A CENTRIFUGAL COMPRESSOR FOR MINIMUM LOSSES AND FLOW DISTORTION

In the Oil & Gas industry, large variations in flow rates are often encountered which require compression trains with a wide operating range. If the stable operating range at constant speed is insufficient, variable speed drivers can be used to meet the requirements. Alternatively, variable guide vanes (IGVs) can be introduced into the inlet plenum to provide pre- or counter-swirl to the first stage impeller, possibly eliminating the need for variable speed. This paper presents the development and validation of circumferentially non-uniform IGVs that were specifically designed to provide maximum angle variation at minimum losses and flow distortion for the downstream impeller. This includes the comparison of three concepts: a baseline design based on circumferentially uniform and symmetric profiles and two circumferentially non-uniform concepts based on uniquely cambered airfoils at each circumferential position and a multi airfoil configuration consisting of a uniquely cambered fixed part and a movable part. The idea behind the circumferentially non-uniform designs was to take into account non-symmetric flow features inside the plenum and a bias towards large preswirl angles rather than counter-swirl during practical operation. The designs were carried out by CFD and first tested in a steady, full-annulus cascade in order to quantify pressure losses and flow quality at the inlet to the impeller at different IGV setting angles (ranging from −20° to +60°) and flow rates. Subsequently, the designs were mounted in front of a typical Oil & Gas impeller on a high speed rotating rig in order to determine the impact of flow distortion on the impeller performance. The results show that pressure losses in the inlet plenum could be reduced by up to 40% with the circumferentially non-uniform designs over the symmetric baseline configuration. Furthermore, a significant reduction in circumferential distortion could be achieved with the circumferentially non-uniform designs. The resulting improvement in impeller performance contributed approx. 40% to the overall efficiency gains for inlet plenum and impeller combined.© 2015 ASME

Annular Cascade for Radial Compressor Development

A full-annulus cascade for radial compressor stator development has been designed and commissioned. The cascade has been developed for the rapid screening of novel stator concepts to facilitate risk mitigation in the early design phase and the validation/calibration of numerical predictions. The rig consists of two main parts. The first part is comprised of an exchangeable set of stationary preswirl vanes that have been designed to mimic discrete points on the operating characteristic of the impeller. The second part consists of a diffuser, bend and return channel with return channel vanes that can also be quickly exchanged. All exchangeable parts are manufactured by rapid prototyping, allowing rapid turnaround times from aerodynamic design to full validation. This is achieved at a significantly lower cost than that of a full rotating test. This investigation summarizes the experimental results and numerical predictions of two test rigs that were designed to study the effect of diffusion ratio, i.e. the ratio of the maximum outer diameter at the top of the bend to the exit of the impeller, on stator performance. To further investigate the sensitivity of the aerodynamic performance to different flow conditions, metal gauzes were positioned immediately downstream of the trailing edges of the preswirl vanes. This allowed the modification of angle and pressure distributions in the diffuser and bend as well as the setting of different turbulence conditions (intensity and length scale) in the downstream sections.© 2011 ASME