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Innovation of Flexible String and Ball-Spine Inverse Design Methods for 2D and Axisymmentric Internal Flows

Nili Ahmadabadi, Mahdi | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40211 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Hajilouy Benisi, Ali; Dor Ali, Mohammad; Ghadak, Farhad
  7. Abstract:
  8. Duct Inverse design problems usually involve finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, a novel iterative inverse design method is presented and developed for internal flows. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall’s pressure distribution is reached. The flow field at each step is analyzed to obtain the current pressure distribution along the wall. This method is developed for inviscid subsonic, transonic and supersonic flow regimes with normal shock (Euler equations) and for viscous incompressible flow regimes with separation (Navier-Stokes equations). Various validation test cases and design examples are presented here which show the robustness and flexibility of the method in handling complex geometries. The method is a physical and quick converging approach and can efficiently utilize commercial flow analysis software. By using the physical base of Flexible String Algorithm (FSA), the second novel inverse design algorithm called Ball-Spine Algorithm (BSA), simpler than FSA, is presented for duct inverse design. In BSA compared to FSA, the unknown walls are composed of a set of virtual balls instead of flexible string that move freely along the specified directions called spines. The difference between the target and current pressure distribution on walls causes the balls to be moved along the spines. Considering that the BSA is an iterative inverse design method, Fluent Software is considered as a flow solver by UDF in Fluent. Also, a quasi-3D and an axisymmetric AUSM code solving Euler equation on the meridional plane of a centrifugal compressor and gas turbine nozzle are incorporated into BSA in order to design of radial impeller hub-shroud profile and nozzle profile. In order to validate the designed shapes, the current centrifugal compressor and nozzle are numerically analyzed in 3D and the numerical results are approved by the experimental results that obtained at Sharif University Gas Turbine Lab. Then, the designed compressor and nozzle are numerically analyzed and the calculated performances are compared to the current performances. The results show that the momentum decrease near the shroud wall in the existing compressor is removed by hub-shroud modification resulting an improvement in performance by 0.7 percent. In addition to improvement of the compressor performance, the nozzle thrust coefficient increases by 2 percent.
  9. Keywords:
  10. Inverse Design ; Two Dimensional Flow ; Axisymmetric Flow ; Centrifugal Compressor ; Aerodynamic Ducts ; Flexible String ; Ball-Spine Algorithm

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