Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sunil Patil ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Mean Flow ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Near Wall

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

2011 ◽  
Author(s):  
Sunil Patil ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Boundary Layer Equation ◽  
Reynolds Numbers ◽  
Wall Region ◽  
Mean Flow ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics ◽  
Wall Boundary Conditions ◽  
Large Eddy ◽  
Near Wall

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the LES framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of Rau et al. [1], and Han et al. [2], and wall resolved LES data of Tafti [3]. Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

Large-Eddy Simulations of Heat Transfer in a Ribbed Channel for Internal Cooling of Turbine Blades

2003 ◽  
Author(s):  
D. K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Mean Flow ◽  
Square Channel ◽  
Nusselt Numbers ◽  
Separated Shear Layer ◽  
Friction Factors ◽  
Large Eddy

Large-Eddy Simulations (LES) are performed in a ribbed square channel with rib height to hydraulic diameter ratio of 0.1, and rib pitch to rib height ratio of 10. The calculations are performed for a nominal bulk Reynolds number of 20,000. Hydrodynamic and thermal fully-developed conditions are assumed. Results from two mesh resolutions, 963 and 1283 are presented and compared to available data in the literature. Time evolution, mean, and turbulent quantities are presented, together with the heat transfer. Both calculations capture the mean flow structures with precision and compare well with experimental data. Turbulent rms quantities also agree extremely well with available measurements. The finer mesh resolves the separated shear layer with greater precision and differences of 10–15% are observed between the two calculations. Similar differences are observed in the predictions of friction factors and Nusselt numbers between the two meshes. The friction factor and Nusselt number are underpredicted when compared to measurements in the literature.

LES Simulation and Experimental Measurement of Fully Developed Ribbed Channel Flow and Heat Transfer

2002 ◽  
Author(s):  
Kazunori Watanabe ◽  
Toshihiko Takahashi
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Rotor Blade ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Ribbed Channel ◽  
Flow And Heat Transfer ◽  
Large Eddy

Ribbed channel flow is adopted for internal cooling of a 1300 °C class gas turbine first stage rotor blade. Heat transfer characteristics of transverse ribbed channel flow were examined using LES (Large Eddy Simulations) and by experiments. The flow was examined over the range of Reynolds number around 105 that are closer to the actual engine conditions. Computational results agreed reasonably well with experimental results. Heat transfer enhancement mechanism in a ribbed channel flow was shown to be caused by advecting eddy structure and interference of a rib.

LES Simulations of Rotating Two-Pass Ribbed Duct With Coriolis and Centrifugal Buoyancy Forces at Re=100,000

2016 ◽  
Author(s):  
Cody Dowd ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Large Eddy Simulations ◽  
The Other ◽  
Coriolis Forces ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Buoyancy Forces ◽  
First Pass ◽  
Duct Geometry

The focus of this research is to predict the flow and heat transfer in a rotating two-pass duct geometry with staggered ribs using Large-Eddy Simulations (LES). The geometry consists of a U-Bend with 17 ribs in each pass. The ribs are staggered with an e/Dh = 0.1 and P/e = 10. LES is performed at a Reynolds number of 100,000, a rotation number of 0.2 and buoyancy parameters (Bo) of 0.5 and 1.0. The effects of Coriolis forces and centrifugal buoyancy are isolated and studied individually. In all cases it is found that increasing Bo from 0.5 to 1.0 at Ro = 0.2 has little impact on heat transfer. It is found that in the first pass, the heat transfer is quite receptive to Coriolis forces which augment and attenuate heat transfer at the trailing and leading walls, respectively. Centrifugal buoyancy, on the other hand has a bigger effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On contrary, it aids heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. The heat transfer in the second pass is dominated by the highly turbulent flow exiting the bend. Coriolis forces have no impact on the augmentation of heat transfer on the leading wall till the second half of the passage whereas it attenuates heat transfer at the trailing wall as soon as the flow exits the bend. Contrary to phenomenological arguments, inclusion of centrifugal buoyancy augments heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass.

scholarly journals A Computational Visualization of Three Dimensional Flow: Finding Optimum Heat Transfer and Pressure Drop Characteristics From Short Cross-Pin Arrays and Comparison With Two Dimensional Calculations

1999 ◽  
Author(s):  
E. E. Donahoo ◽  
C. Camci ◽  
A. K. Kulkarni ◽  
A. D. Belegundu
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Structural Integrity ◽  
Turbine Blades ◽  
Circular Cross Section ◽  
Internal Cooling ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
Spacing Ratio ◽  
Cooling Passage

There are many heat transfer augmentation methods that are employed in turbine blade design, such as impingement cooling, film cooling, serpentine passages, trip strips, vortex chambers, and pin fins. The use of crosspins in the trailing edge section of turbine blades is commonly a viable option due to their ability to promote turbulence as well as supply structural integrity and stiffness to the blade itself. Numerous crosspin shapes and arrangements are possible, but only certain configurations offer high heat transfer capability while maintaining taw total pressure loss. This study preseots results from 3-D numerical simulations of airflow through a turbine blade internal cooling passage. The simulations model viscous flow and heat transfer over full crosspins of circular cross-section with fixed height-to-diameter ratio of 0.5, fixed transverse-to-diameter spacing ratio of 1.5, and varying streamwise spacing. Preliminary analysis indicates that endwall effects dominate the flow and heat transfer at lower Reynolds numbers. The flow dynamics involved with the relative dose proximity of the endwalls for such short crosspins have a definite influeoce on crosspin efficiency for downstream rows.

Large-Eddy Simulations of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Dario Amirante ◽  
Nicholas J. Hills
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Outer Radius ◽  
Large Eddy Simulations ◽  
Test Cases ◽  
Mean Flow ◽  
Flow Equations ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Least Squares Approach

Large-eddy simulations (LES) of wall bounded, low Mach number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES (ILES) procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds number Reb = 44 × 103 based on the pipe diameter, and a confined rotor–stator flow at the rotational Reynolds number ReΩ = 4 × 105 based on the outer radius. In both cases, the mean flow and the turbulent statistics agree well with existing direct numerical simulations (DNS) or experimental data.

Numerical Optimization, Characterization, and Experimental Investigation of Additively Manufactured Communicating Microchannels

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Kathryn L. Kirsch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Transport Systems ◽  
Optimized Design ◽  
Internal Cooling ◽  
Natural Systems ◽  
Flow And Heat Transfer ◽  
Successful Replication

The degree of complexity in internal cooling designs is tied to the capabilities of the manufacturing process. Additive manufacturing (AM) grants designers increased freedom while offering adequate reproducibility of microsized, unconventional features that can be used to cool the skin of gas turbine components. One such desirable feature can be sourced from nature; a common characteristic of natural transport systems is a network of communicating channels. In an effort to create an engineered design that utilizes the benefits of those natural systems, the current study presents wavy microchannels that were connected using branches. Two different wavelength baseline configurations were designed; then each was numerically optimized using a commercial adjoint-based method. Three objective functions were posed to (1) minimize pressure loss, (2) maximize heat transfer, and (3) maximize the ratio of heat transfer to pressure loss. All baseline and optimized microchannels were manufactured using laser powder bed fusion (L-PBF) for experimental investigation; pressure loss and heat transfer data were collected over a range of Reynolds numbers. The AM process reproduced the desired optimized geometries faithfully. Surface roughness, however, strongly influenced the experimental results; successful replication of the intended flow and heat transfer performance was tied to the optimized design intent. Even still, certain test coupons yielded performances that correlated well with the simulation results.

A Comparative Study of DES and URANS in a Two-Pass Internal Cooling Duct With Normal Ribs

2005 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Detached Eddy Simulation ◽  
Mean Flow ◽  
Streamline Curvature ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Developing Flow

The capabilities of the Detached Eddy Simulation (DES) and the Unsteady Reynolds Averaged Navier-Stokes (URANS) versions of the 1988 κ-ω model in predicting the turbulent flow field and the heat transfer in a two-pass internal cooling duct with normal ribs is presented. The flow is dominated by the separation and reattachment of shear layers; unsteady vorticity induced secondary flows and strong streamline curvature. The techniques are evaluated in predicting the developing flow at the entrance to the duct and downstream of the 180° bend, fully-developed regime in the first pass, and in the 180° bend. Results of mean flow quantities, secondary flows, friction and heat transfer are compared to experiments and Large-Eddy Simulations (LES). DES predicts a slower flow development than LES, while URANS predicts it much earlier than LES computations and experiments. However it is observed that as fully developed conditions are established, the capability of the base model in predicting the flow and heat transfer is enhanced by switching to the DES formulation. DES accurately predicts the flow and heat transfer both in the fully-developed region as well as the 180° bend of the duct. URANS fails to predict the secondary flows in the fully-developed region of the duct and is clearly inferior to DES in the 180° bend.

Computation of flow and heat transfer through channels with periodic dimple/protrusion walls using low-Reynolds number turbulence models

2019 ◽  
Vol 29 (3) ◽  
pp. 1178-1207 ◽  
Author(s):  
Mohammad Fazli ◽  
Mehrdad Raisee
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Correction Term ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Internal Cooling ◽  
Recirculation Bubble ◽  
Content Type ◽  
Flow And Heat Transfer ◽  
Numerical Predictions

PurposeThis paper aims to predict turbulent flow and heat transfer through different channels with periodic dimple/protrusion walls. More specifically, the performance of various low-Rek-ε turbulence models in prediction of local heat transfer coefficient is evaluated.Design/methodology/approachThree low-Re numberk-εturbulence models (the zonalk-ε, the lineark-εand the nonlineark-ε) are used. Computations are performed for three geometries, namely, a channel with a single dimpled wall, a channel with double dimpled walls and a channel with a single dimple/protrusion wall. The predictions are obtained using an in house finite volume code.FindingsThe numerical predictions indicate that the nonlineark-εmodel predicts a larger recirculation bubble inside the dimple with stronger impingement and upwash flow than the zonal and lineark-εmodels. The heat transfer results show that the zonalk-εmodel returns weak thermal predictions in all test cases in comparison to other turbulence models. Use of the lineark-εmodel leads to improvement in heat transfer predictions inside the dimples and their back rim. However, the most accurate thermal predictions are obtained via the nonlineark-εmodel. As expected, the replacement of the algebraic length-scale correction term with the differential version improves the heat transfer predictions of both linear and nonlineark-εmodels.Originality/valueThe most reliable turbulence model of the current study (i.e. nonlineark-εmodel) may be used for design and optimization of various thermal systems using dimples for heat transfer enhancement (e.g. heat exchangers and internal cooling system of gas turbine blades).

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