Numerical Simulations of the Near-Field Region of Film Cooling Jets Under High Free Stream Turbulence: Application of RANS and Hybrid URANS/Large Eddy Simulation Models

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Free Stream ◽  
Near Field ◽  
Turbulent Heat ◽  
Field Region ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Large Eddy

This paper investigates the flow field and thermal characteristics in the near-field region of film cooling jets through numerical simulations using Reynolds-averaged Navier–Stokes (RANS) and hybrid unsteady RANS (URANS)/large eddy simulation (LES) models. Detailed simulations of flow and thermal fields of a single-row of film cooling cylindrical holes with 30 deg inline injection on a flat plate are obtained for low (M = 0.5) and high (M = 1.5) blowing ratios under high free stream turbulence (FST) (10%). The realizable k‐ε model is used within the RANS framework and a realizable k‐ε-based detached eddy simulation (DES) is used as a hybrid URANS/LES model. Both models are used together with the two-layer zonal model for near-wall simulations. Steady and time-averaged unsteady film cooling effectiveness obtained using these models are compared with available experimental data. It is shown that hybrid URANS/LES models (DES in the present paper) predict more mixing both in the wall-normal and spanwise directions compared to RANS models, while unsteady asymmetric vortical structures of the flow can also be captured. The turbulent heat flux components predicted by the DES model are higher than those obtained by the RANS simulations, resulting in enhanced turbulent heat transfer between the jet and mainstream, and consequently better predictions of the effectiveness. Nevertheless, there still exist some discrepancies between numerical results and experimental data. Furthermore, the unsteady physics of jet and crossflow interactions and the jet lift-off under high FST is studied using the present DES results.

Simulation of the Near-Field Region of Film Cooling Jets Using RANS and Hybrid URANS/LES Models

2014 ◽  
Author(s):  
Hosein Foroutan ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Free Stream ◽  
Near Field ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Field Region ◽  
Detached Eddy Simulation ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence

This paper investigates the flow field and heat transfer in the near-field region of film cooling jets through numerical simulations using RANS and hybrid URANS/LES models. Detailed simulations of flow and thermal fields of a single row of film cooling cylindrical holes with 30° inline injection on a flat plate are obtained for low (M = 0.5) and high (M = 1.5) blowing ratios under high free stream turbulence (10%). The realizable k-ε model is used within the RANS framework and a realizable k-ε-based detached eddy simulation (DES) is used as a hybrid URANS/LES model. Both models are used together with the two-layer zonal model for near-wall simulations. Steady and time-averaged unsteady film cooling effectiveness obtained using these models in ANSYS-FLUENT are compared with available experimental data. It is shown that hybrid URANS/LES models (DES in the present paper) predict more mixing both in the wall-normal and spanwise directions compared to RANS models, while unsteady asymmetric vortical structures of the flow can also be captured. The turbulent heat flux components predicted by the DES model are higher than those obtained by the RANS simulations, resulting in enhanced turbulent heat transfer between the jet and mainstream, and consequently better predictions of the effectiveness. Furthermore, the unsteady physics of jet and crossflow interactions and the jet lift-off under high free stream turbulence is studied using the present DES results.

Large Eddy Simulation of Leading Edge Film Cooling: Part I — Computational Domain and Effect of Coolant Pipe Inlet Condition

2007 ◽  
Author(s):  
Ali Rozati ◽  
Danesh K. Tafti
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Free Stream ◽  
Leading Edge ◽  
Driving Mechanism ◽  
Computational Domain ◽  
Stagnation Line ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Pipe Inlet

A numerical investigation is conducted to study compound angle leading edge film cooling with Large Eddy Simulation. The leading edge has two rows of coolant holes located at ±15° of the stagnation line. Coolant jets are injected into the flow field at 30° (span-wise) and 90° (stream-wise). Mainstream Reynolds number is 100,000 based on the free stream velocity and cylinder diameter. Jet to mainstream velocity and density ratios are 0.4 and 1.0, respectively. It is found that during startup the stagnation line at the leading edge is not stationary but moves on a timescale much larger than the characteristic turbulent scales generated by the jet-mainstream interaction. To alleviate the long time integration necessitated by this feature, only half the domain is calculated (fixed stagnation) by showing that there is very little correlation in the flow structures generated by the jet-mainstream interaction on either side of stagnation. A comparison is made between a laminar uniform profile at the coolant pipe inlet with a time-dependent turbulent profile extracted from an auxiliary turbulent pipe flow calculation. The former over-predicts the span-wise averaged effectiveness, while the latter promotes better mixing in the outer region of jet-mainstream interaction and lowers the adiabatic effectiveness showing good agreement with measurements. In both cases, a characteristic low frequency interaction between the jet and the mainstream is identified at a non-dimensional frequency between 0.79 and 0.95 based on jet diameter and velocity. Even in the absence of any free-stream and jet turbulence, a turbulent boundary layer is established within a diameter downstream of the jet due to the strong lateral entrainment downstream of injection. The entrainment is primarily driven by an asymmetric counterrotating vortex pair in the immediate wake of the coolant jet. The driving mechanism for the formation of these vortices is a low pressure zone in the wake which entrains mainstream flow laterally into this region.

Large-Eddy Simulation of Interacting Film Cooling Jets

2009 ◽  
Author(s):  
Peter Renze ◽  
Wolfgang Schro¨der ◽  
Matthias Meinke
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Plate Thickness ◽  
Turbulent Heat Transfer ◽  
Numerical Dissipation ◽  
Turbulent Heat ◽  
Eddy Simulation ◽  
Large Eddy

In the present paper the flow field of a film cooling configuration with three staggered rows of holes is investigated using large-eddy simulations (LES). The numerical method uses the MILES approach (monotone-integrated large-eddy simulation) and the discretization of the governing equations is based on a mixed central-upwind AUSM (advective upstream splitting method) scheme with low numerical dissipation. The current investigations focus on full-coverage film cooling with finest drilling holes. The film cooling configuration consists of three staggered rows of holes with a lateral hole spacing of p/D = 3 and a streamwise row distance of l/D = 6. The inclination angle of the cooling holes is α = 30° and the flat plate thickness is h/D = 12. The cooling hole exit geometry is fanshaped with lateral and streamwise expansions. The results evidence the different nature of the mixing process between the jets and the crossflow after the first, second, and third row. The turbulent kinetic energy peaks at the interaction region of the undisturbed boundary layer with the first row. The low velocity ratio leads to reduced velocity gradients in the lower boundary layer downstream of the first row. Thus, the turbulence production is reduced at the interaction with the following rows. The adiabatic film cooling effectiveness is substantially improved after the second and third injection and the decay of effectiveness is reduced, respectively. The turbulent heat transfer is investigated and strong variations of the turbulent Prandtl number are evident in the flow field.

scholarly journals Loss Prediction in an Axial Compressor Cascade at Off-Design Incidences With Free Stream Disturbances Using Large Eddy Simulation

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
John Leggett ◽  
Stephan Priebe ◽  
Aamir Shabbir ◽  
Vittorio Michelassi ◽  
Richard Sandberg ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Free Stream ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Boundary Layer Transition ◽  
Compressor Cascade ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Profile Losses ◽  
Large Eddy

Axial compressors may be operated under off-design incidences due to variable operating conditions. Therefore, a successful design requires accurate performance and stability limits predictions under a wide operating range. Designers generally rely both on correlations and on Reynolds-averaged Navier–Stokes (RANS), the accuracy of the latter often being questioned. The present study investigates profile losses in an axial compressor linear cascade using both RANS and wall-resolved large eddy simulation (LES), and compares with measurements. The analysis concentrates on “loss buckets,” local separation bubbles and boundary layer transition with high levels of free stream turbulence, as encountered in real compressor environment without and with periodic incoming wakes. The work extends the previous research with the intention of furthering our understanding of prediction tools and improving our quantification of the physical processes involved in loss generation. The results show that while RANS predicts overall profile losses with good accuracy, the relative importance of the different loss mechanisms does not match with LES, especially at off-design conditions. This implies that a RANS-based optimization of a compressor profile under a wide incidence range may require a thorough LES verification at off-design incidence.

scholarly journals Large Eddy Simulation of Film Cooling with Bulk Flow Pulsation: Comparative Study of LES and RANS

2020 ◽  
Vol 10 (23) ◽  
pp. 8553
Author(s):  
Seung Il Baek ◽  
Joon Ahn
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Streamwise Velocity ◽  
Bulk Flow ◽  
Flow Pulsation ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy

The effects of bulk flow pulsations on film cooling in gas turbine blades were investigated by conducting large eddy simulation (LES) and Reynolds-averaged Navier–Stokes simulation (RANS). The film cooling flow fields under 32 Hz pulsation in the mainstream from a cylindrical hole inclined 35° to a flat plate at the average blowing ratio of M = 0.5 were numerically simulated. The LES results were compared to the experimental data of Seo, Lee, and Ligrani (1998) and Jung, Lee, and Ligrani (2001). The credibility of the LES results relative to the experimental data was demonstrated through a comparison of the time-averaged adiabatic film cooling effectiveness, time- and phase-averaged temperature contours, Q-criterion contours, time-averaged velocity profiles, and time- and phase-averaged Urms profiles with the corresponding RANS results. The adiabatic film cooling effectiveness predicted using LES agreed well with the experimental data, whereas RANS highly overpredicted the centerline effectiveness. RANS could not properly predict the injectant topology change in the streamwise normal plane, but LES reproduced it properly. In the case of the injectant trajectory, which greatly influences film cooling effectiveness, RANS could not properly predict the changes in the streamwise velocity peak due to flow pulsation, but they were predicted well with LES. RANS greatly underpredicted the streamwise velocity fluctuations, which determine the mixing of main flow and injectant, whereas LES prediction was close to the experimental data.

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