Thermo-Structural Analysis of a Roots Expander


Preethi R.S.
Giridhar M Jambare
Sonil Singh
Swaminathan Subramanian


Roots expander is a waste heat recovery device that utilizes the pressure energy from the engine exhaust to produce useful work. It is mounted downstream of the engine and consists of a housing with a pair of twisted rotors that are separated from each other by fine clearances. As the expander is exposed to high temperature exhaust gases from the engine, there will be deformations primarily caused by thermal expansion. There can be variable deformations of the parts (owing to different materials) resulting in change in clearances that can affect the performance of this device. Thus, it is important to understand the thermo-structural behavior of expander, which is the motivation behind the present work. This paper will detail the methodology that was used to model the thermo-structural behavior of expander using CFD & FE analysis. A co-simulation method was adopted to couple transient CFD analysis with steady state FE thermal simulations to get the temperature distribution on the device. The obtained temperature results are then used in steady state FE structural analysis to determine the deformations. A macro & Microsoft Excel based clearance calculator was developed to determine the clearance change based on the deformation results. Based on the change in clearances, necessary modifications can be made to the design of expander to achieve optimum efficiency.


How to Cite
Preethi R.S., Giridhar M Jambare, Sonil Singh, & Swaminathan Subramanian. (2022). Thermo-Structural Analysis of a Roots Expander. ARAI Journal of Mobility Technology, 2(4), 392–400.


  1. Lemort, Vincent, Ludovic Guillaume, Arnaud Legros, Sébastien Declaye, and Sylvain Quoilin. "A comparison of piston, screw and scroll expanders for small scale Rankine cycle systems." In The 3rd international conference on microgeneration and related technologies. 2013.
  2. Hsu, Sung-Wei, Hsiao-Wei D. Chiang, and Chih-Wei Yen. 2014. "Experimental Investigation of the Performance of a Hermetic Screw-Expander Organic Rankine Cycle" Energies 7, no. 9: 6172-6185.
  3. Wang, Wei & Wu, Yuting & Ma, Chong-fang & Xia, Guo-dong & Wang, Jing-Fu. (2013). Experimental study on the performance of single screw expanders by gap adjustment. Energy. 62. 379-384.
  4. Stretch, Dale, Wright, Brad, Fortini, Matt, Fink, Neal, Ramadan, Bassem, and Eybergen, William. 2016. "Roots Air Management System with Integrated Expander". United States.
  5. Fan, Q., Kuba, M., and Nakanishi, J., "Coupled Analysis of Thermal Flow and Thermal Stress of an Engine Exhaust Manifold," SAE Technical Paper 2004-01-1345, 2004,
  6. Spille-Kohoff, A., Hesse, J., Andres, R., “Twin Mesh Grid Generator and CFD Simulations with Ansys CFX,” 2nd short course on CFD in rotary positive displacement machines,, accessed September 2016.
  7. Hesse, J., “Webinar: TwinMesh for reliable CFD analysis of rotating positive displacement machines”, accessed September 2016.
  8. Gonella, R., Peselli, V., “Thermal-Structural Analysis of Cylinder Head using Workbench Platform as Unique Calculation Environment.” 4th European Automotive Simulation Conference, July 2009.
  9. Deshpande, Shrikrishna, Himanshu Joshi, Jaiganesh Madhavan, Paul Mason, and Carlos Wink. "Two-way coupled CFD approach for predicting gear temperature of oil jet lubricated transmissions." SAE International Journal of Commercial Vehicles 11, no. 3 (2018): 163-170.,
  10. ANSYS, CFX-Pre, CFD simulation software, User’s Guide, Solver Theory Guide.
  11. ANSYS, FE Modeler User’s Guide.
  12. ANSYS, Mechanical APDL, Advanced Analysis Guide.