Effects of Non-Axisymmetric Volute On Rotating Stall in the Vaneless Diffuser of Centrifugal Compressors

Rotating stall is an important unstable flow phenomenon that leads to performance degradation and limits the stability boundary in centrifugal compressors. The volute is one of the sources inducing non-axisymmetric flows in centrifugal compressors, which has an important effect on compressors' aerodynamic performance. However, the influence of volute on rotating stall is unclear. Therefore, the effects of volute on rotating stall behavior have been explored in this paper by experiments and numerical simulations. The frequency of the rotating stall captured by the experiments is 43.9% of the impeller passing frequency, while it is 44.7% of IPF calculated from the numerical results, which proves the accuracy and capability of the numerical method in this work to study the rotating stall behavior. The flow fields from CFD simulations further reveal that one stall cell initializing in a particular location deforms into several stall cells while rotating along the circumferential direction and becomes much smaller in a specific location during the evolution process, and finally, it is suppressed in another specific location as a result of the distorted flow field caused by the volute. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that the rotating stall can be weakened or suppressed, which is helpful to extend the stable operating range of centrifugal compressors.

Searching for the Most Suitable Loss Model Set for Subsonic Centrifugal Compressors Using an Improved Method for Off-Design Performance Prediction

This work investigates loss model sets based on empirical loss correlations for subsonic centrifugal compressors. These loss models in combination with off-design performance prediction algorithms make up an essential tool in predicting off-design behaviour of turbomachines. This is important since turbomachines rarely work under design conditions. This study employs an off-design performance prediction algorithm based on an iterative process from Galvas. Modelling of ten different loss mechanisms and physical phenomena is involved in this approach and is thoroughly described in this work. Geometries of two subsonic compressors were reconstructed and used in the evaluation of individual loss correlations in order to obtain a suitable loss model. Results of these variations are compared to experimental data. In addition, 4608 loss model sets were created by taking all possible combinations of individual loss estimations from which three promising candidates were selected for further investigation. Finally, off-design performance of both centrifugal compressors was computed. These results were compared to experimental data and to other loss model sets from literature. The newly composed loss model set No. 2137 approximates experimental data over a 21.2% better in relative error than the recent Zhang set and nearly a 36.7% better than the outdated Oh’s set. Therefore, set No. 2137 may contribute to higher precision of centrifugal turbomachines’ off-design predictions in the upcoming research.

Monitoring the structural condition of parts of K 250 centrifugal compressors at different stages of production

Among the existing methods of ensuring the production of goods, an important place is occupied by the input and final quality control of metal products in production. The main task of the input control is to constantly ensure the necessary level of quality, fixed in regulatory documents, by directly checking each batch of supplied metal. The use of active quality control directly during the production of goods allows to prevent and detect defects at the initial stages and during the manufacture of finished types of metal products. Control at the output of the production system has the main purpose to prevent the transfer of defective products to the consumer or to the subsequent technological phases (stages). Goal. The goals is development of methods for monitoring the parts of K-250 centrifugal compressors at various stages of production and selection of the optimal mode of heat treatment of rotor elements made of structural steel of the martensitic class of the 34KHN1MA brand. Method. The control included mechanical tests, metallographic studies of blanks and finished parts, as well as non-destructive testing for internal defects and surface quality. Results. A comprehensive input control of the macro- and microstructure, as well as the mechanical properties of blanks made of 34KHN1MA steel was carried out. A mode of improving the properties of critical parts of a centrifugal compressor made of 34KHN1MA steel by heat treatment is proposed. Control of the finished product was carried out, including mechanical tests, microstructure studies, as well as non-destructive surface quality control.

Sensitivity analysis of centrifugal compressors aerodynamic losses using 1D-mean streamline prediction technique

One-dimensional modeling and prediction of the centrifugal compressor performance are challenging as they require conservation equations and empirical and semi-empirical correlations. Therefore, there is a need to perform a consolidated study of the compressor aerodynamic loss models to conclude the importance of each loss to the compressor performance modeling. Accordingly, the purpose of this paper is to examine the effect of each aerodynamic loss on the compressor performance and explore more about which loss could have a negligible effect on the compressor performance. A MATLAB code was developed to predict the performance of five different small turbocharger centrifugal compressors at different geometric and operating conditions. The developed code was validated using the available experimental data of the investigated compressors. A sensitivity analysis methodology was performed using the validated code to check the effect of ten aerodynamic losses for the impeller and volute sections on the compressor performance. This paper concludes that impeller disk friction, blade loading, and clearance losses have a negligible effect on the small turbocharger vanless diffuser compressor performance.

Turbo/Supercharger Compressors and Turbines for Aircraft Propulsion in WWII: Theory, History and Practice—Guidance from the Past for Modern Engineers and Students

This book is a unique blend of history, technology review, theoretical fundamentals, and design guide. The subject matter is primarily piston aeroengine superchargers – developed in Germany during the Second World War (WWII) – which are centrifugal compressors driven either by the main engine crankshaft or by an exhaust gas turbine. The core of the book is an unpublished manuscript by Karl Kollmann, who was a prominent engineer at Daimler-Benz before and during the war. Dr. Kollmann’s manuscript was discovered by Calum Douglas during his extensive research for his earlier book on piston aeroengine development in WWII. It contains a wealth of information on aerothermodynamic and mechanical design of centrifugal compressors in the form of formulae, charts, pictures, and rules of thumb, which, even 75 years later, constitute a valuable resource for engineering professionals and students. In addition to the translation of the original manuscript from German, the authors have completely overhauled the chapters on the aerothermodynamics of centrifugal compressors so that the idiosyncratic coverage (characteristic of German scientific literature at that time) is familiar to a modern reader. Furthermore, the authors added chapters on exhaust gas turbines (for turbo-superchargers), piston aeroengines utilizing them, and turbojet gas turbines. Drawing upon previously unpublished material from the archived German documents, those chapters provide a concise but technically precise and informative look into those technologies, where great strides were made in Germany during the war. In summary, the coverage is intended to be useful not only to history buffs with a technical bent but also to the practicing engineers and engineering students to help with their day-to-day activities in this particular field of turbomachinery.

Basic Theory of Centrifugal Compressors

This chapter is where Dr. Kollmann’s original manuscript starts. His introduction of the fundamental aerothermodynamic principles governing the design of centrifugal (radial) compressors is not in a form that one would find in standard textbooks, vintage or modern. Dr. Kollmann essentially lists the pertinent equations in the form of a ‘crib sheet’ that an experienced engineer would consult in his or her daily work. This is not surprising because, in all likelihood, when he was writing this manuscript (or at least this part of it) Dr. Kollmann did not have access to all his papers and books. In fact, the authors have a suspicion (a rather strong one from the cover page, as shown in the title page of the present book) that Dr. Kollmann wrote this section while he was actually in Allied custody or at ‘home supervision’.

Numerical investigation of the diffuser throat length effect on a transonic centrifugal compressor

Vaned diffuser inlet flow uniform is challenging when the impeller is throttled to stall. In this study, we extend the stable operating range of the compressor by improving the uniform flow of the diffuser inlet. First, a numerical investigation of a transonic centrifugal compressor with a vaned diffuser is presented and compared against test data. Then, a new diffuser parameterization method is pro- posed, and the throat feature of a pipe diffuser is successfully applied to parameterized vane diffusers. The influence of the throat length and divergence angle of the diffuser on the performance of the centrifugal compressor is studied via steady and non-linear harmonic simulations. Throat length delays the time of fluid pressurization and accommodates large flow instabilities from upstream—this widens the stall margin but increases mixing loss. Divergence angle affects compressor performance. Stage peak efficiency increases by about 0.58% as the divergence angle increases from 3.79° to 5.79° but drops to about 2.46% as the divergence angle further increases from 5.79° to 11.79°. This is because the boundary layers in the diffuser channel thicken with increasing divergence angle; additionally, the fluid near the hub-pressure side first becomes unstable, then flow separation occurs along the flow direction, which results in a large flow loss. Detailed performance maps of centrifugal compressors with different throat lengths and divergence angles are given to provide a reference for designing transonic centrifugal compressors.