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Large-Eddy Simulation and Active Flow Control of Low-Reynolds Number Flow through a Low-Pressure Turbine Cascade

POONDRU, SHIRDISH

Abstract Details

2008, PhD, University of Cincinnati, Engineering : Mechanical Engineering.

The operating Reynolds numbers (Re) for a low-pressure turbine (LPT) in an aircraft engine can drop below 25,000 during high-altitude cruise conditions, resulting in massive separation and subsequent transition on the blade suction surface. This separation causes a significant loss in the engine efficiency. Hence, accurate prediction of the flow physics at these low-Re conditions is required to effectively implement flow control techniques which can help mitigate separation-induced losses. The present work investigated this low-Re transitional flow through a LPT cascade comprised of the generic Pratt & Whitney “PAKB” blades, using high-order accurate compact numerical schemes in conjunction with large-eddy simulation (LES), with and without subgrid-scale (SGS) models. The study examined the predictive capability of the explicit Smagorinsky and dynamic Smagorinsky SGS models, as compared to the Implicit LES (ILES) technique (LES without an explicit SGS model). The research also implemented active flow control on the LPT blades using momentum injection via surface blowing. All simulations utilized a dual-topology, multi-block, structured grid, and computations were performed on a massively parallel computing platform using MPI-based communications. The baseline cases (without control) were simulated at Re ~ 10,000, 25,000 and 50,000. The computed numerical results for all three cases showed good agreement with available experimental data. The Smagorinsky and dynamic Smagorinsky SGS model results provided no significant improvement over the ILES results because of the low level of energy in the subgrid-scales for the present low-Re flow conditions investigated, and hence, the ILES technique was used for all subsequent flow-control simulations.

Separation control of the LPT flow was implemented using synthetic normal jets, synthetic vortex-generator jets, and pulsed vortex-generator jets (VGJs) at Re ~ 10,000, for four blowing ratios ranging from 0.5 to 4.7, where the blowing ratio is defined as the ratio of the jet-exit velocity magnitude to the local free-stream velocity. All the jets were implemented by specifying an analytical boundary condition at the jet exit surface. The effectiveness of the jets was assessed in terms of the integrated wake loss coefficient values, and the modified Zweifel coefficient values. The Zweifel coefficient represents the component of the integrated blade Cp distribution contributing to the direction of rotation. Among the three types of control jets implemented, the synthetic normal jets were found to be more effective than the synthetic or pulsed VGJs. For pulsed VGJs, the effective blowing ratio was found to be 2.0 in the present study, compared to the value of 0.4 documented in the literature for control at a Re = 25,000, indicating a strong dependence of the effective blowing ratio on Re. The study also examined the flow control mechanisms of the synthetic normal jets and vortex-generator jets. It was found that the mechanism for effectiveness of synthetic jets was a combination of instability-triggered transition and free-stream momentum entrainment. Finally, the synthetic jets and synthetic VGJs were found to be more effective when the jets were located just upstream of the natural separation point.

Urmila Ghia (Advisor)
186 p.

Recommended Citations

Citations

  • POONDRU, S. (2008). Large-Eddy Simulation and Active Flow Control of Low-Reynolds Number Flow through a Low-Pressure Turbine Cascade [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204873699

    APA Style (7th edition)

  • POONDRU, SHIRDISH. Large-Eddy Simulation and Active Flow Control of Low-Reynolds Number Flow through a Low-Pressure Turbine Cascade. 2008. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204873699.

    MLA Style (8th edition)

  • POONDRU, SHIRDISH. "Large-Eddy Simulation and Active Flow Control of Low-Reynolds Number Flow through a Low-Pressure Turbine Cascade." Doctoral dissertation, University of Cincinnati, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204873699

    Chicago Manual of Style (17th edition)