Contact Analysis of Impeller-Shaft assembly and Reasonably Designing the Amount Interference of Turbocompressors

Abstract

The interference fit between impeller and shaft assembly is one of the most important factors influencing the performance of the turbo unit in the design of turbocompressors. The assembly creates a complicated frictional contact problem the interface of the mating parts when the rotational speed is high. Therefore, stress analysis and suitable amount of interference need to be considered in the structural design. A locomotive-type turbocompressor with 24 blades is used for the present analysis. The FE parametric quadratic programming (PQP) method which was developed based on the parametric variational principle (PVP) is used for the analysis of the stress distribution of 3-D frictional contact problem of impeller-shaft sleeve-shaft, makes it possible to precisely simulate complicated geometrical shapes of impeller and considerably enhances accuracy in computation. The advantages of the parametric programming method as compared with the conventional ones are that the penalty factors can be cancelled and the solutions can be obtained directly without tedious iterative procedures such as general incremental iterative method[1]. The effects of fit tolerance and rotational speed, the displacement and the contact stress on the interference-fitting surfaces are discussed in detail in this paper. A range of friction coefficients in the impeller-shaft sleeve and shaft sleeve-shaft contact interfaces is investigated in order to represent the mechanical behaviors of the structure due to the change of the interface characteristic. To decrease the difficulty of the assembling process and make sure the safety of the working state, the suitable amount of the interference is studied so that the interface can have adequate contact pressure under full load. It is found that nonuniform initial interference value in the structural design would avoid relative displacement generated and ensure uniformity of the contact stress. To assure quality of press-fitting, the amount of interference between the shaft sleeve and shaft by press-fitting should be controlled strictly to avoid the rapid increase of the contact stress. The study provides an effective approach which achieves more reliable interference-fitted connections and more precise assembly accuracy with lower manufacturing cost in the structural design.