A Review of Turbine and Compressor Aerodynamic Forces in Turbomachinery

Abstract

Aerodynamic forces due to blade-tip clearance eccentricity are a known destabilizing source in rotating machinery with unshrouded impellers. Dynamic forces also appear in shrouded impellers, due to changes in the pressure in the gap between the impeller casing and its shroud. These are load-dependent forces typically characterized by a cross-coupled stiffness coefficient (k > 0). This paper reviews the archival literature for quantification of blade-tip clearance induced forces and impeller-casing forces in both unshrouded and shrouded turbines and compressors. Most distinctive are the lack of experimental results and the indiscriminate application of simple formulas to predict k, including Alford’s and Wachel’s equations. The disparity in estimations of the destabilizing k extends to recent CFD models and results. Hence, rotordynamic predictions vary widely. This review reveals that engineering practice ignores accurate physical models that could bridge the gap between practice and theory. As the energy market shifts toward carbon capture and hydrogen compression, accurate knowledge of aerodynamic forces from unshrouded compressors and open impellers will become necessary in multi-stage rotors.

Impact of Gas Foil Bearings, Labyrinth Seals, and Impellers on the Critical Speed of Centrifugal Compressors for Fuel Cell Vehicles: A Comprehensive Investigation

“…The Wachel equation [33,34] has been verified by a large number of practices, has been listed by the American Petroleum Institute (API) as the standard calculation method in the stability calculation process of centrifugal compressors [47], and is applicable to most compressors [30]. In this study, the Wachel equation is used to calculate the aerodynamic cross-coupling stiffness of the impeller, and the rest of the rotordynamic coefficients are set to 0.…”

“…For the impeller, blade-tip clearance eccentricity due to shaft movement can lead to the generation of aerodynamic forces [30]. This phenomenon is commonly referred to as the Alford force in compressors [31].…”

Building of a Mathematical Model for Solving the Elastic–Gas-Dynamic Task of the Gas Lubrication Theory for Petal Bearings

“…The development of a petal gas-dynamic bearing (PGDB) that combines the idea of a bearing with a pliable surface and a bearing with self-aligning sector inserts dates back to 1963. A review of archival research focused on assessing the load characteristics quantitatively and the problem of ignoring accurate physical models in engineering practice is presented in [1]. The stages of the development of gas-lubricated support structures are discussed in more detail in [2].…”