Flow and Heat Transfer in the Tip-Turn Region of a U-Duct Under Rotating and Non-Rotating Conditions

2011 ◽  
Author(s):  
S.-Y. Hu ◽  
X. Chi ◽  
T. I.-P. Shih ◽  
K. M. Bryden ◽  
M. K. Chyu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Computational Study ◽  
Reynolds Numbers ◽  
Coolant Temperature ◽  
Internal Cooling ◽  
Wall Functions ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Turn Region

CFD simulations were performed to study the flow and heat transfer in a U-duct, relevant to internal cooling of the first-stage turbine component in electric-power-generation, gas-turbine engines. Parameters studied include (1) two aspect ratios of the duct cross section, i.e. H/W = 1 and H/W = 0.25; (2) smooth duct and duct lined with pin fins of height H arranged in a staggered fashion; and (3) two rotational speeds: 0 rpm and 3,600 rpm. In all cases, the wall temperature is 1173 K; the coolant temperature at the U-duct inlet is 623 K; and the back pressure at the exit of the U-duct is 25.17 atm. The Reynolds numbers studied are 150,000 for the duct with the 4-to-1 aspect ratio, and 150,000 and 375,000 for the duct with the 1-to-1 aspect ratio. When there is rotation at 3,600 rpm, the rotational numbers corresponding to these Reynolds numbers and duct aspect ratios are 0.592, 1.64, and 4.11, respectively. Result is presented to show the nature of the flow, the temperature distribution, and the surface heat transfer with focus on the flow and heat transfer in the tip-turn region as a function of the parameters investigated. This computational study is based on 3-D steady RANS. The ensemble-averaged continuity, compressible Navier-Stokes, and energy equations were closed by the thermally perfect equation of state with temperature-dependent gas properties and the two-equation realizeable k-ε turbulence model with and without wall functions.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Periodic Fluid Flow and Heat Transfer in a Square Cavity Due to an Insulated or Isothermal Rotating Rectangular Object

2009 ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
H.-W. Dai ◽  
Liwu Fan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Angular Velocity ◽  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Constant Angular Velocity ◽  
Square Cavity ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Aspect Ratios

Computational analysis of transient phenomenon followed by the periodic state of laminar flow and heat transfer due to a rectangular rotating object in a square cavity is investigated. A finite-volume-based fixed-grid/sliding mesh computational methodology utilizing primitive variables is used. Rectangular rotating objects with different aspect ratios (AR = 1, 2, 3, 4) are placed in the middle of a square cavity. The motionless object is set in rotation at time t = 0 with a constant angular velocity. For the insulated and isothermal objects, the cavity is maintained as differentially-heated and isothermal enclosures, respectively. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr = 5 fluid. The Reynolds numbers were selected so that the flow field is not affected by the Taylor instabilities (Ta < 1750). The periodic flow field, the interaction of the rotating objects with the recirculating vortices at the four corners and the periodic channelling effect of the traversing vertices are clearly elucidated. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. Transient variations of the average Nusselt numbers of the respective systems show that for high Re numbers, a quasi-periodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt numbers of the insulated and isothermal object systems were correlated to the rotational Reynolds number and the aspect ratio of the rectangle. For high Re numbers, the performance of the system is independent of the aspect ratio. On the other hand, with lowering of the hydraulic diameter (i.e. bigger objects), objects with the highest and lowest aspect ratios exhibit the highest and lowest heat transfer, respectively. High intensity of the periodic channelling and not its frequency are identified as the cause of the observed enhancement.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45 deg to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100–0.058 for AR 1:1–1:6, respectively. The experiments span a Reynolds number range of 4000–130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

scholarly journals Computations of Flow and Heat Transfer in a Channel With Rows of Hemispherical Cavities

1999 ◽  
Author(s):  
Y.-L. Lin ◽  
T. I-P. Shih ◽  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Computational Study ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Wall Functions ◽  
Time Stepping ◽  
Flow And Heat Transfer ◽  
A Cell ◽  
Volume Method

Computations were performed to investigate the three-dimensional flow and heat transfer in a high aspect ratio channel in which one or two wall are lined with four rows of hemispherical cavities arranged in a staggered fashion with two Reynolds numbers (23,000 and 46,000). The focus is on understanding the flow induced by cavities and how that flow affects surface heat transfer. Computed results were compared with available experimental data. This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy closed by the low Reynolds number shear-stress transport k-ω turbulence model (wall functions were not used). Solutions were generated by a cell-centered finite-volume method that uses third-order accurate flux-difference splitting of Roe with limiters, multigrid acceleration of a diagonalized ADI scheme with local time stepping, and patched/overlapped structured grids.

Numerical Simulation of Flow and Heat Transfer in Rectangular Channel With Different Aspect Ratios

2016 ◽  
Author(s):  
Liu Wenhua ◽  
Mo Yang ◽  
Li Ling ◽  
Qiao Liang ◽  
Yuwen Zhang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Characteristic Length ◽  
Rectangular Channel ◽  
Equivalent Diameter ◽  
Correction Coefficient ◽  
Corner Region ◽  
Flow And Heat Transfer ◽  
Aspect Ratios

Turbulent flow and heat transfer in rectangular channel has an important significance in engineering. Conventional approach to caculate Nusselt number of rectangular channel approximately is to take the equivalent diameter as the characteristic length and use the classic circular channel turbulent heat transfer coefficient correlations. However, under these conditions, the caculation error of Nusselt number can reach to 14% and thus this approach can not substantially describe the variation of Nusselt number of rectangular cross-sections with different aspect ratios. Therefore, caculation by using equivalent diameter as the characteristic length in classic experiment formula needs to be corrected. Seven groups of rectangular channel models with different aspect ratios have been studied numerically in this paper. By using standard turbulence model, the flow and heat transfer law of air with varing properties has been studied in 4 different sets of conditions in Reynolds number. The simulation and experimental results are in good agreement. The simulation results show that with the increase of aspect ratio, the cross-sectional average Nusselt number increased, Nusselt number of circumferential wall distributed more evenly and the difference between the infinite plate channel and square channel went up to 25%. The effects of corner region and long\short sides on heat transfer have also been investigated in this paper. Results show that in rectangular channel, heat transfer in corner region is significantly weaker than it in other region. With the increase of aspect ratio, effect on the long side of heat transfer of the short side is gradually reduced, and then eventually eliminates completely in the infinite flat place. Based on the studies above, correction coefficient for rectangular channels with different aspect ratios has been proposed in this paper and the accuracy of the correction coefficient has been varified by numerical simulations. This can reflect the variation of Nusselt number under different aspect ratios more effectively and thus has current significance for project to calculate Nusselt number of heat transfer in rectangular channel.

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.

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.

Numerical Simulation of Flow and Heat Transfer in Rotating Cooling Passage With Turning Vane in Hub Region

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Hung-Chieh Chu ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Complex Flow ◽  
Flow And Heat Transfer ◽  
Cooling Passage ◽  
Turn Region

Numerical simulation of three-dimensional turbulent flow and heat transfer was performed in a multipass rectangular (AR = 2:1) rotating cooling channel with and without turning vane in the hub region under various flow conditions, with two different Reynolds numbers of 10,000 and 25,000, two different channel orientations of 45-deg and 90-deg, and the rotation number varies from 0 to 0.2. This study shows that the addition of the turning vane in the hub turn region does not cause much impact to the flow before the hub. However, it significantly alters the flow reattachment and vortex distribution in the hub turn region and after the hub turn portion. The local heat transfer is deeply influenced by this complex flow field and this turning vane effect lasts from the hub turn region to the portion after it.

Laminar Fluid Flow and Heat Transfer in a Lid-Driven Cavity Due to a Thin Fin

2002 ◽  
Vol 124 (6) ◽  
pp. 1056-1063 ◽  
Author(s):  
Xundan Shi ◽  
J. M. Khodadadi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Computational Study ◽  
Reynolds Numbers ◽  
Left Wall ◽  
Driven Cavity ◽  
Flow And Heat Transfer ◽  
Heat Transfer Capacity ◽  
The Right ◽  
Steady Laminar

A finite-volume-based computational study of steady laminar flow and heat transfer (neglecting natural convection) within a lid-driven square cavity due to a single thin fin is presented. The lid moves from left to right and a fixed thin fin can be positioned perpendicular to any of the three stationary walls. Three fins with lengths equal to 5, 10, and 15 percent of the side, positioned at 15 locations were examined for Re=500, 1000, 2000, and Pr=1 (total of 135 cases). Placing a fin on the right wall brings about multi-cell recirculating vortices compared to the case without a fin that exhibits a primary vortex and two small corner cells. A fin slows the flow near the anchoring wall and reduces the temperature gradients, thus degrading heat transfer capacity. A fin positioned near the top right corner of the cavity can reduce heat transfer most effectively in cases with all three different Reynolds numbers and lengths. Regardless of the Reynolds number, placing a fin on the right wall—compared to putting a fin on the left and bottom walls—can always enhance heat transfer on the left wall and at the same time, reduce heat transfer on the bottom, right and top walls. A long fin has the most marked effect on the system’s heat transfer capabilities. Mean Nusselt number was successfully correlated to the Reynolds number, length of the fin and its position.

Investigations on Nusselt Number Enhancement in Ribbed Rectangular Turbine Blade Cooling Channels of Different Aspect Ratios and Rotation Numbers

2013 ◽  
Author(s):  
Behnam Nouri ◽  
Knut Lehmann ◽  
Arnold Kühhorn
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Turbine Blade ◽  
High Heat ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Aspect Ratios ◽  
Number Distribution ◽  
Nusselt Number Distribution

In the drive for higher cycle efficiencies in gas turbine engines, turbine blades are seeing an increasingly high heat load. This in turn demands improvements in the internal cooling system and a better understanding of both the level and distribution of the internal heat-transfer. A typical approach to enhance the internal cooling of the turbine blade is by casting angled ‘low blockage’ ribs on the walls of the cooling channels. The objective of the present paper is to determine the detailed Nusselt number distribution in rectangular internal channels with ribs. This knowledge can be used to guide the overall design e.g. to achieve high levels of heat-transfer where required. The effects of rotation as well as the interaction effects of the position and direction of ribs on opposite walls of the cooling channel have been investigated. Numerical calculations have been carried out using the commercial CFD code Fluent to investigate the local Nusselt number enhancement factor in rectangular ducts of different aspect ratios (0.5, 1 and 2) which have 45° or 90° angled ribs located on two opposite walls. This has been studied for different Rotation number Ro (0–0.45) and with a Reynolds number >30000. The first series of studies has been carried out with the same experimental setup as by Han [1]. The geometry was slightly changed to avoid the effect of high heat transfer at the entry. This study identifies important vortical structures, which are dependent on the direction and the position of the ribs. This has a profound effect on the distribution of heat-transfer within the passage. It is shown that the two smooth walls of the duct have different average Nusselt number ratio Nu/NuFD enhancement depending on the rib angle. In addition, based on numerical investigations, simple correlations have been developed for the rotational influence of the internal Nusselt number distribution. A major finding is that the effect of rotation is dominant for low aspect ratio channels and the local enhancement due to the rib position and angle is more dominant for high aspect ratio channels.

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