Analysis of Gas Turbine Rotating Cavities by an One-Dimensional Model

Abstract

Reliable design of secondary air system is one of the main tasks for the safety, unfailing and performance of gas turbine engines. To meet the increasing demands of gas turbines design, improved tools in prediction of the secondary air system behavior over a wide range of operating conditions are needed. A real gas turbine secondary air system includes several components, therefore its analysis is not carried out through a complete CFD approach. Usually, that predictions are performed using codes, based on simplified approach which allows to evaluate the flow characteristics in each branch of the air system requiring very poor computational resources and few calculation time. Generally the available simplified commercial packages allow to correctly solve only some of the components of a real air system and often the elements with a more complex flow structure cannot be studied; among such elements, the analysis of rotating cavities is very hard. This paper deals with a design-tool developed at the University of Florence for the simulation of rotating cavities. This simplified in-house code solves the governing equations for steady one-dimensional axysimmetric flow using experimental correlations both to incorporate flow phenomena caused by multidimensional effects, like heat transfer and flow field losses, and to evaluate the circumferential component of velocity. Although this calculation approach does not enable a correct modeling of the turbulent flow within a wheel space cavity, the authors tried to create an accurate model taking into account the effects of inner and outer flow extraction, rotor and stator drag, leakages, injection momentum and, finally, the shroud/rim seal effects on cavity ingestion. The simplified calculation tool was designed to simulate the flow in a rotating cavity with radial outflow both with a Batchelor and/or Stewartson flow structures. A primary 1D-code testing campaign is available in the literature [1]. In the present paper the authors develop, using CFD tools, reliable correlations for both stator and rotor friction coefficients and provide a full 1D-code validation comparing, due to lack of experimental data, the in house design-code predictions with those evaluated by CFD.

Measurement and Prediction of Centrifugal Compressor Axial Forces During Surge—Part II: Dynamic Surge Model

“…Lately, Baldassarre, et al [30] have developed 1D software to estimate radial pressure distribution along impeller surfaces, and subsequently, the total axial thrust acting on the rotor; they validate the model using the experimental data from two highpressure centrifugal compressors tested at full load. In that work they used the correlation of Da Soghe, et al [31].…”

Time accurate modelling of the secondary air system response to rapid transients

“…It is recommended that some investigation of the flow field is attempted by means of CFD or rig testing. In particular, Da Soghe et al [23] showed the usefulness of CFD to characterize the vortex in a rotating cavity for a range of operating conditions. On the other hand, the time scales of the problem under scrutiny would require expensive and complicated experimental testing.…”

A Novel Method for Developing Compressor’s Characteristic Curves Due to the Guide Vane Stagger Angle Variation

“…A well designed one-dimensional model could monitor the detailed behavior of the gas turbines components in real-time. Such models are very effective in real-world control systems and are being used in power and electricity generation plants [1][2][3][4]. Air compressor as one of the main components of gas turbines has to be modeled in one-dimensional form, while gas turbine is being modeled as one-dimensional [5].…”