CFD MODELING TO STUDY THE EFFECT OF SPACER DESIGN ON CENTRIFUGAL COMPRESSOR EXIT SCROLL PERFORMANCE

Present day Centrifugal Compressor (CC) technology trend is moving towards innovative designs for improved performance. Computational Fluid Dynamics (CFD) plays an important role in the assessment and improvement of CC component design. Statoric parts like inlet plenum, diffuser, return channel, and exit scroll play a vital role in determining the overall performance of any compressor. Exit scrolls (volute) are an integral part of any CC. A volute is essentially a flow collecting duct with its cross-section area increasing around the circumference as more volume of fluid is added. There are different types of volutes used for CC based on the type of application, casing size and the site conditions. The performance of a volute is very important in terms of magnitude of losses, static pressure recovery as well as impact on the upstream impeller. It is essential that the volute is well matched with the impeller and diffuser at the best stage efficiency point. In addition to that, some obstructions needed for mechanical purposes (spacers, bolts, grooves) result in more losses, decreasing overall compressor efficiency affecting severely the upstream impeller. The purpose of this paper is to describe an extensive CFD analysis that was performed to understand and quantify the negative impact arising due to the presence of spacers, their shapes and circumferential location on the performance of the whole compressor. The paper is divided into two sections. First section describes the CFD studies to understand performance of a typical scroll with spacers (boat tail spacers) as obstacles and effect of tangential location of spacers. The second section describes the CFD studies to understand the impact of the shape of spacers in a comparative manner.