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Research Papers

Application of Unsteady Computational Fluid Dynamics Methods to Trailing Edge Cutback Film Cooling

[+] Author and Article Information
Silvia Ravelli

Department of Engineering,
University of Bergamo,
Marconi Street 5,
Dalmine BG 24044, Italy
e-mail: silvia.ravelli@unibg.it

Giovanna Barigozzi

Department of Engineering,
University of Bergamo,
Marconi Street 5,
Dalmine BG 24044, Italy
e-mail: giovanna.barigozzi@unibg.it

Contributed by the International Gas Turbine Institute (IGTI) Division of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 14, 2014; final manuscript received July 18, 2014; published online August 26, 2014. Editor: Ronald Bunker.

J. Turbomach 136(12), 121006 (Aug 26, 2014) (11 pages) Paper No: TURBO-14-1142; doi: 10.1115/1.4028238 History: Received July 14, 2014; Revised July 18, 2014

The main purpose of this numerical investigation is to overcome the limitations of the steady modeling in predicting the cooling efficiency over the cutback surface in a high pressure turbine nozzle guide vane. Since discrepancy between Reynolds-averaged Navier–Stokes (RANS) predictions and measured thermal coverage at the trailing edge was attributable to unsteadiness, Unsteady RANS (URANS) modeling was implemented to evaluate improvements in simulating the mixing between the mainstream and the coolant exiting the cutback slot. With the aim of reducing the computation effort, only a portion of the airfoil along the span was simulated at an exit Mach number of Ma2is = 0.2. Three values of the coolant-to-mainstream mass flow ratio were considered: MFR = 0.66%, 1.05%, and 1.44%. Nevertheless the inherent vortex shedding from the cutback lip was somehow captured by the URANS method, the computed mixing was not enough to reproduce the measured drop in adiabatic effectiveness η along the streamwise direction, over the cutback surface. So modeling was taken a step further by using the scale adaptive simulation (SAS) method at MFR = 1.05%. Results from the SAS approach were found to have potential to mimic the experimental measurements. Vortices shedding from the cutback lip were well predicted in shape and magnitude, but with a lower frequency, as compared to particle image velocimetry (PIV) data and flow visualizations. Moreover, the simulated reduction in film cooling effectiveness toward the trailing edge was similar to that observed experimentally.

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References

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Figures

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Fig. 1

Vane and trailing edge cooling geometry (size in mm) [20]

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Fig. 2

3D computational domain and boundary conditions

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Fig. 3

Views of the grid at midspan with monitor points for convergence evaluation

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Fig. 4

Snapshots of flow visualizations (left) and URANS instantaneous predictions (right) of the normalized temperature contours θ at midspan for ((a) and (b)) MFR = 0.66%, ((c) and (d)) MFR = 1.05%, and ((e) and (f)) MFR = 1.44%

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Fig. 5

Instantaneous measurements (left) and URANS predictions (right) of the normalized spanwise vorticity at midspan for ((a) and (b)) MFR = 0.66% and ((c) and (d)) MFR = 1.44%

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Fig. 6

Experimental measurements (Exp.), RANS, instantaneous (Inst.) and time averaged (T.A.) URANS predictions of the adiabatic effectiveness η at MFR = 0.66% ((a)–(c)), 1.05% ((d)–(h)), and 1.44% ((i)–(m)), together with oil and dye surface flow visualizations (vis.)

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Fig. 7

Instantaneous SAS contours of the normalized temperature θ at midspan, for MFR = 1.05%

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Fig. 8

Instantaneous (a) URANS and (b) SAS contours of the normalized spanwise vorticity at midspan, for MFR = 1.05%

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Fig. 9

Instantaneous (a) URANS and (b) SAS contours of the normalized turbulent viscosity μt/μ at midspan, for MFR = 1.05%

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Fig. 10

(a) URANS and (b) SAS isosurface of Q = 5*107s−2 colored by the normalized spanwise vorticity, for MFR = 1.05%

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Fig. 11

(a) Instantaneous and (b) time averaged SAS predictions of the adiabatic effectiveness η at MFR = 1.05%

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Fig. 12

Measurements (exp.) and predictions of the adiabatic effectiveness η along the cutback centerline, at MFR = 1.05%

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Fig. 13

Measurements (exp.) and predictions of the laterally averaged adiabatic effectiveness ηav along the cutback surface, at MFR = 1.05%

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