Aerodynamic Functional Diagnostics Based on Angular Momentum Transport Lines

In analogy with the classical concept of mass-flux-based streamlines, we define angular momentum transport (AMT) lines as an aerodynamic functional diagnostic tool. The AMT lines are the ones whose tangents are given by the average angular momentum flux. The mathematical and physical properties of these AMT lines are exploited to study the generation, removal, and transport of angular momentum in turbomachinery components. We illustrate the concept by visualizing AMT lines in two relatively simple flows, namely, vaneless incompressible diffuser and von Karman flow (a model of centrifugal compressors). Next, we apply the proposed diagnostic tool to flow in a return channel. A return channel is a part of a multistage centrifugal compressor stage. Its principal function is to remove angular momentum. In this work, we apply the diagnostic tool of AMT lines to a Reynolds-averaged Navier Stokes (RANS) simulation and a wall-modeled large eddy simulation (LES) of flow in the return channel. We show that AMT lines give us insights into the AMT process that are otherwise not available with conventional visualization tools.

Aerodynamic Functional Diagnostics Based on Angular Momentum Transport Lines

In analogy with the classical concept of mass-flux-based streamlines, we define Angular Momentum Transport (AMT) lines as an aerodynamic functional diagnostic tool. The AMT lines are the ones whose tangents are given by the average angular momentum flux. The mathematical and physical properties of these AMT lines are exploited to study the generation, removal, and transport of angular momentum in turbomachinery components. We illustrate the concept by visualizing AMT lines in two relatively simple flows, namely, vaneless incompressible diffuser and von Karman flow (a model of centrifugal compressors). Next, we apply the proposed diagnostic tool to flow in a return channel. A return channel is a part of a multistage centrifugal compressor stage. Its principal function is to remove angular momentum. In this work, we apply the diagnostic tool of AMT lines to a Reynolds averaged Navier Stokes simulation (RANS) and a wall-modeled large eddy simulation (LES) of flow in the return channel. We show that AMT lines give us insights into the angular momentum transport process that are otherwise not available with conventional visualization tools.

Numerical Investigation on Labyrinth Seal Leakage Flow and Its Effects on Aerodynamic Performance for a Multistage Centrifugal Compressor

Labyrinth seals are widely used in industrial centrifugal compressors to reduce leakage. However, no work has been conducted to numerically investigate the detailed seal leakage flow and its effects in an environment of multistage centrifugal compressor. To clarify the flow mechanism of leakage flow and the interaction mechanism between leakage and mainstream flow in multistage centrifugal compressors, the flow of the last two stages from a four-stage centrifugal compressor is studied using computational fluid dynamics (CFD) model with and without considerations of labyrinth seal leakage paths, i.e., two shroud seals, one interstage seal, and one balance piston seal. The results show that the leakage flow in shroud and hub cavities can be described as a Batchelor-type flow. The Ekman number of the cavity Batchelor flow is small and corresponds to thin boundary layers while the Rossby number is at unity order implying the importance of rotating effects. The leakage flow through the shroud, interstage, and balance piston labyrinth seals is decreased by the combined effects of throttling and diffusion flow, and has distinctive flow structures associated with the type of labyrinth seal. The influence of leakage flow on the mainstream flow can be described by suction or injection mode. The suction mode is beneficial to the improvement of mainstream flow quality while the injection mode is harmful. This work is of scientific significance to enrich the knowledge of internal fluid mechanics and of potential application value to control and design the leakage flow in real configurations of multistage centrifugal compressors.

Analysis of Rotordynamic and Thermodynamic Performance of a Multistage Centrifugal Compressor Operating in the Minimum Flow Region

In this paper both rotordynamic and thermodynamic analysis of a multistage centrifugal compressor running with one or more stages in post-stall condition are presented. The purpose of this study is to demonstrate the machine can operate stable and safe in such condition (i.e. stable condition means the head vs. flow operating curve shall have negative slope and safe means a vibration free machine). This allows to extend the operating range at lower flow with respect to the current day-by-day design practice. Experimental results from ASME PTC10 Class 2 test carried out on a seven-stage compressor are shown to validate the analysis.