Session: 01-01-01: Advanced Structural Mechanics and Computational Methods for Aerospace Applications

Paper Number: 183101

183101 - Structural Analysis and Experimental Validation of a Spline Coupling in a Turbopump Shaft Assembly 

Turbopumps are fluid pump systems that deliver the fuel and oxidizer fluids with the required flow rate and pressure to the combustion chamber using their high power. These systems generally consist of three main components: a fuel pump, an oxidizer pump, and a turbine mounted on a shaft assembly. The critical design issues are torque transmission reliability under high rotational speeds, extreme temperatures, and large torques. Factors such as stress distribution, misalignment, and thermal expansion strongly influence system performance, operational lifespan, and overall stability. Consequently, the structural design of connecting components, particularly spline couplings, are crucial for the dependable operation of turbopumps.

Spline couplings are commonly employed in turbopump shaft assemblies due to their high torque capacity and ability to accommodate axial displacements with small alignment errors. Through well-designed spline geometries, concentricity errors can be reduced, thermal expansion differences compensated, and load distribution made uniform. Nevertheless, manufacturing tolerances create uncertainty in the number of torque-transmitting teeth, making the load-sharing behavior difficult to predict. Furthermore, high stress concentrations at tooth roots result from high torque and dynamic load variations in turbopumps. Therefore, accurate and optimal design requires both finite element analysis (FEA) and experimental validation. In this study, a structural analysis and experimental investigation of a spline coupling used in a turbopump shaft set are presented. The turbopump shaft assembly, composed of the fuel shaft, oxidizer shaft, and counter shaft, is made of Inconel to ensure compatibility with cryogenic and high-temperature conditions. A dedicated test setup was designed to replicate operational torque transmission between the shafts. Strain gauges were placed at critical tooth root regions identified via FEA, and torque and strain data were recorded under different load levels.

Three-dimensional nonlinear contact analyses were performed using ANSYS APDL. The numerical model replicated experimental boundary conditions and torque loads to obtain torsional behavior and load transfer characteristics. The experimental results are higher than the strain values ​​under nominal torque observed in the FEA analyses. This result obtains from manufacturing tolerances represented by the peak stress factor. When the analyses are updated using this factor which means validating the model, the experimental and numerical results converge significantly.

Transmitting high torques within limited packages in complex and demanding systems like turbopumps is a challenging problem. Creating a reliable analysis model for the spline connections use for this purpose increases confidence in the design. However, relying on an analysis model for an uncertain structure like a spline is difficult. Therefore, a reliable analysis model is created with the test setup. Thus, the validated analysis model provides a reliable method for evaluating spline coupling behavior in turbopump applications. This approach increases confidence in the analysis model and serves as a reference for future turbopump spline design studies without the need for detailed retesting.

Presenting Author: Suna Deniz Roketsan Roket Sanayi ve Ticaret A.S.

Presenting Author Biography: Suna Deniz received her B.Sc. degree in Aeronautical Engineering from Istanbul Technical University, where she is currently pursuing her M.Sc. degree in the same field. She works as a Turbopump Development Engineer at Roketsan, focusing on propulsion systems, fluid mechanics, and turbomachinery design and analysis.