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Low Pressure Turbine Flow Control with Vortex Generator Jets

Williams, Charles P
http://orcid.org/0000-0001-6425-7874
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470741489

Abstract Details

2016, MS, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
In an aircraft engine at high altitude, the low-pressure turbine (LPT) section can experience low-Reynolds number (Re) flows making the turbine blades susceptible to large separation losses. These losses are detrimental to the performance of the turbine and lead to a roadblock for “higher-lift” blade designs. Accurate prediction of the separation characteristics and an understanding of mitigation techniques are of the utmost importance. The current study conducts simulations of flow control techniques for the Air Force Research Laboratory (AFRL) L2A turbine blade at low-Re of 10,000 based on inlet velocity and blade axial chord. This blade was selected for its “high-lift” characteristics coupled with massive separation on the blade at low-Re which provides an excellent test blade for flow control techniques. Flow control techniques involved various configurations of vortex generator jets (VGJs) using momentum injection (i.e. jet blowing). All computations were executed on dual-topology, multi-block, structured meshes and incorporated the use of a parallel computing platform using the message passing interface (MPI) communications. A high-order implicit large eddy simulation (ILES) approach was used in the simulations allowing for a seamless transition between laminar, transitional, and turbulent flow without changing flow solver parameters. A validation study was conducted involving an AFRL L1A turbine blade which showed good agreement with experimental trends for cases which controlled separation in the experiments. The same cases showed good agreement between different grid sizes. The differences between experimental and numerical results are largely attributed to differences in the setup. That is, the simulation did not include freestream turbulence or wind-tunnel wall effects. The flow control study conducted for the L2A blade showed a small degree of separation control for jets placed just downstream (DS) of the separation point. A limited study was conducted with jets moved upstream (US) of the natural separation point which showed an increase in effectiveness for one of the VGJs. This indicates a sensitivity of VGJ location relative to the point of separation. For the DS VGJs, separation control, increased as blowing ratio (BR) was increased and jet blowing frequency (F+) decreased. The increase in jet efficacy with decreasing F+ was unexpected and is mostly attributed to the jets being downstream of the separation location and having a low duty cycle (10%). Turbulent kinetic energy frequency spectra also show the presence of jet harmonics in the flow downstream of the best performing VGJs which dramatically increased in power when the VGJ was moved upstream. The most effective jet found in this study had BR=3.0, F+=3.02, and was located at x/Cx=0.53. This VGJ provided a 42.1% reduction in normalized integrated wake loss. One follow-on simulation was conducted taking the most effective VGJ and increasing the blowing ratio from BR=3.0 to 8.0. This provided a decrease in the amount of separation, nearly eliminating separation with only a small separation bubble remaining. This VGJ was able to provide a 42.8% reduction in normalized integrated wake loss. This work was conducted in coordination with the AFRL and has been approved for public release, case number: 88ABW-2016-1657.
Kirti Ghia, Ph.D. (Committee Chair)
Rolf Sondergaard, Ph.D. (Committee Member)
Shaaban Abdallah, Ph.D. (Committee Member)
Urmila Ghia, Ph.D. (Committee Member)
196 p.
Aerospace Materials
Low Pressure Turbine; Vortex Generator Jet; Active Flow Control; Implicit Large Eddy Simulation; L2A; Low Reynolds Number Flow

Recommended Citations

Citations

  • Williams, C. P. (2016). Low Pressure Turbine Flow Control with Vortex Generator Jets [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470741489

    APA Style (7th edition)

  • Williams, Charles. Low Pressure Turbine Flow Control with Vortex Generator Jets. 2016. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470741489.

    MLA Style (8th edition)

  • Williams, Charles. "Low Pressure Turbine Flow Control with Vortex Generator Jets." Master's thesis, University of Cincinnati, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470741489

    Chicago Manual of Style (17th edition)

ucin1470741489
455
© 2016, some rights reserved.Creative Commons License Low Pressure Turbine Flow Control with Vortex Generator Jets by Charles P Williams is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Cincinnati and OhioLINK.