scholarly journals Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
J. E. Kingery ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
High Intensity ◽  
Gas Turbines ◽  
Large Scale ◽  
Large Diameter ◽  
Leading Edge ◽  
Test Surface ◽  
Bypass Transition ◽  
Stagnation Region ◽  
Heat Transfer Augmentation

Current land-based gas turbines are growing in size producing higher approach flow Reynolds numbers at the leading edge of turbine nozzles. These vanes are subjected to high intensity large scale turbulence. This present paper reports on the research which significantly expands the parameter range for stagnation region heat transfer augmentation due to high intensity turbulence. Heat transfer measurements were acquired over two constant heat flux test surfaces with large diameter leading edges (10.16 cm and 40.64 cm). The test surfaces were placed downstream from a new high intensity (17.4%) mock combustor and tested over an eight to one range in approach flow Reynolds number for each test surface. Stagnation region heat transfer augmentation for the smaller (ReD = 15,625–125,000) and larger (ReD = 62,500–500,000) leading edge regions ranged from 45% to 81% and 80% to 136%, respectively. These data also include heat transfer distributions over the full test surface compared with the earlier data acquired at six additional inlet turbulence conditions. These surfaces exhibit continued but more moderate acceleration downstream from the stagnation regions and these data are expected to be useful in testing bypass transition predictive approaches. This database will be useful to gas turbine heat transfer design engineers.

The Influence of Leading Edge Diameter on Stagnation Region Heat Transfer Augmentation Including Effects of Turbulence Level, Scale, and Reynolds Number

2011 ◽  
Author(s):  
P. Gandavarapu ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Test Surface ◽  
Bypass Transition ◽  
Stagnation Region ◽  
Heat Transfer Augmentation ◽  
Wide Range ◽  
Turbulence Condition ◽  
Level Scale

Stagnation region heat transfer measurements have been acquired on two large cylindrical leading edge test surfaces having a four to one range in leading edge diameter. Heat transfer measurements have been acquired for six turbulence conditions including three grid conditions, two aero-combustor conditions, and a low turbulence condition. The data have been run over an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 110% in the stagnation region for the large leading edge. However, the heat transfer results for the large cylindrical leading edge do not appear to infer a significant level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL parameter. These results indicate that the intensification of approaching turbulence is more prevalent with the more rapid straining of the smaller leading edge. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.

The Influence of Leading Edge Diameter on Stagnation Region Heat Transfer Augmentation Including Effects of Turbulence Level, Scale, and Reynolds Number

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Preethi Gandavarapu ◽  
Forrest E. Ames
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Test Surface ◽  
Bypass Transition ◽  
Stagnation Region ◽  
Heat Transfer Augmentation ◽  
Wide Range ◽  
Turbulence Condition ◽  
Level Scale

Stagnation region heat transfer measurements have been acquired on two large cylindrical leading edge test surfaces having a four to one range in leading edge diameter. Heat transfer measurements have been acquired for six turbulence conditions including three grid conditions, two aero-combustor conditions, and a low turbulence condition. The data have been run over an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 110% in the stagnation region for the large leading edge. However, the heat transfer results for the large cylindrical leading edge do not appear to infer a significant level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL parameter. These results indicate that the intensification of approaching turbulence is more prevalent with the more rapid straining of the smaller leading edge. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.

scholarly journals Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels

2015 ◽  
Author(s):  
J. E. Kingery ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Bypass Transition ◽  
Stagnation Region ◽  
Heat Transfer Augmentation ◽  
Wide Range ◽  
High Turbulence ◽  
Very High ◽  
Turbulence Generator

A database for stagnation region heat transfer has been extended to include heat transfer measurements acquired downstream from a new high intensity turbulence generator. This work was motivated by gas turbine industry heat transfer designers who deal with heat transfer environments with increasing Reynolds numbers and very high turbulence levels. The new mock aero-combustor turbulence generator produces turbulence levels which average 17.4%, which is 37% higher than the older turbulence generator. The increased level of turbulence is caused by the reduced contraction ratio from the liner to the exit. Heat transfer measurements were acquired on two large cylindrical leading edge test surfaces having a four to one range in leading edge diameter (40.64 cm and 10.16 cm). Gandvarapu and Ames [1] previously acquired heat transfer measurements for six turbulence conditions including three grid conditions, two lower turbulence aero-combustor conditions, and a low turbulence condition. The data are documented and tabulated for an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 136% in the stagnation region for the large leading edge. This heat transfer rate is an increase over the previous aero-combustor turbulence generator which had augmentation levels up to 110%. Note, the rate of increase in heat transfer augmentation decreases for the large cylindrical leading edge inferring only a limited level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL (Turbulence, Reynolds number, Length scale) parameter. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.

scholarly journals The Influence of Large Scale High Intensity Turbulence on Vane Heat Transfer

1995 ◽  
Author(s):  
Forrest E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Intensity ◽  
Large Scale ◽  
Grid Turbulence ◽  
Absolute Level ◽  
Relative Level ◽  
Stagnation Region ◽  
Pressure Surface ◽  
Heat Transfer Augmentation

An experimental research program was undertaken to examine the influence of large scale high intensity turbulence on vane heat transfer. The experiment was conducted in a four vane linear cascade at exit Reynolds numbers of 500,000 and 800,000 based on chord length corresponding to exit Mach numbers of 0.17 and 0.27. Heat transfer measurements were made for four inlet turbulence conditions including a low turbulence case (Tu ≅ 1%), a grid turbulence case (Tu ≅ 7.5%), and two levels of large scale turbulence generated with a mock combustor at two upstream locations (Tu ≅ 12% & Tu ≅ 8%). The heat transfer data demonstrated that the length scale, Lu, has a significant effect on stagnation region and pressure surface heat transfer. The average heat transfer augmentation over the pressure surface was found to scale reasonably well on the relative level of dissipation. The stagnation region heat transfer correlated well on the {Tu ReD5/12 (Lu/D)−1/3} parameter of Ames and Moffat (1990). The dependence of heat transfer augmentation on Reynolds number was estimated to scale on the 1/3 power for the pressure surface. The absolute level of heat transfer augmentation was found to be highest near the stagnation region. The combustor closely coupled to the cascade produced an average augmentation on the pressure surface of 56 percent at a Reynolds number of 800,000.

The Response of High Intensity Turbulence in the Presence of Large Stagnation Regions

2013 ◽  
Author(s):  
N. Chowdhury ◽  
F. E. Ames
Keyword(s):  
High Intensity ◽  
Strain Field ◽  
Large Scale ◽  
Large Diameter ◽  
Leading Edge ◽  
Wave Number ◽  
Inertial Subrange ◽  
Small Scale ◽  
Wall Region ◽  
Stagnation Region

Relatively small scale turbulence is known to intensify in the presence of a stagnation region due to the elongation of these eddies by the mean strain field of the approach flow. Experimental evidence also demonstrates that the large scale eddies are blocked as they approach presence of the stagnation surface. Recent heat transfer measurements suggest that very high intensity turbulence or turbulence in the presence of very large scale leading edge regions may not be as strongly influenced by the stagnation region strain field. Understanding the physics of turbulence is critical to the improvement of turbulence models which are used to predict the surface heat load in gas turbine hot sections. This paper documents the response of high intensity turbulence in the approach flow of two large cylindrical leading edge regions. Measurements of turbulence intensity, scale, spectra, and dissipation have been acquired for five elevated levels of turbulence in the approach flow of two large diameter (0.1016 m and 0.4064 m) leading edge regions. Generally, three influences were observed. Initially, in the presence of the largest cylinder the smaller scale higher intensity turbulence showed increased decay due to longer effective convection times. Secondly, dissipation levels, as estimated from the inertial subrange of the one-dimensional spectra, initially decreased then increased as the strain field intensified in the presence of the stagnation regions. Finally, the measurements indicated that the energy in the low wave number spectra was increasingly blocked in the near wall region of the leading edge.

scholarly journals Influence of Turbulence Parameters, Reynolds Number, and Body Shape on Stagnation-Region Heat Transfer

1995 ◽  
Vol 117 (3) ◽  
pp. 597-603 ◽  
Author(s):  
G. J. Van Fossen ◽  
R. J. Simoneau ◽  
C. Y. Ching
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Velocity Gradient ◽  
Isotropic Turbulence ◽  
Leading Edge ◽  
Length Scale ◽  
Stagnation Region ◽  
Free Stream Turbulence ◽  
Heat Transfer Augmentation ◽  
Optimum Scale

This experiment investigated the effects of free-stream turbulence intensity, length scale, Reynolds number, and leading-edge velocity gradient on stagnation-region heat transfer. Heat transfer was measured in the stagnation region of four models with elliptical leading edges downstream of five turbulence-generating grids. Stagnation-region heat transfer augmentation increased with decreasing length scale but ann optimum scale was not found. A correlation was developed that fit heat transfer data for isotropic turbulence to within ±4 percent but did not predict data for anisotropic turbulence. Stagnation heat transfer augmentation caused by turbulence was unaffected by the velocity gradient. The data of other researchers compared well with the correlation. A method of predicting heat transfer downstream of the stagnation point was developed.

The Influence of Large-Scale High-Intensity Turbulence on Vane Heat Transfer

1997 ◽  
Vol 119 (1) ◽  
pp. 23-30 ◽  
Author(s):  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
High Intensity ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Grid Turbulence ◽  
Stagnation Region ◽  
Linear Cascade ◽  
Pressure Surface ◽  
Scale Turbulence

An experimental research program was undertaken to examine the influence of large-scale high-intensity turbulence on vane heat transfer. The experiment was conducted in a four-vane linear cascade at exit Reynolds numbers of 500,000 and 800,000 based on chord length. Heat transfer measurements were made for four inlet turbulence conditions including a low turbulence case (Tu ≅ 1 percent), a grid turbulence case (Tu ≅ 7.5 percent), and two levels of large-scale turbulence generated with a mock combustor at two upstream locations (Tu ≅ 12 percent and 8 percent). The heat transfer data demonstrated that the length scale, Lu, has a significant effect on stagnation region and pressure surface heat transfer.

Stagnation Line Heat Transfer Augmentation Due to Freestream Vortical Structures and Vorticity

2002 ◽  
Vol 124 (3) ◽  
pp. 583-587 ◽  
Author(s):  
Aung N. Oo ◽  
Chan Y. Ching
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Freestream Turbulence ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Vortical Structures ◽  
Heat Transfer Augmentation

An experimental study has been performed to investigate the effect of freestream vortical structures and vorticity on stagnation region heat transfer. A heat transfer model with a cylindrical leading edge was tested in a wind tunnel at Reynolds numbers ranging from 67,750 to 142,250 based on leading edge diameter of the model. Grids of parallel rods were placed at several locations upstream of the heat transfer model in orientations where the rods were perpendicular and parallel to the stagnation line to generate freestream turbulence with distinct vortical structures. All three components of turbulence intensity, integral length scale and the spanwise and transverse vorticity were measured to characterize the freestream turbulence. The measured heat transfer data and freestream turbulence characteristics were compared with existing empirical models for the stagnation line heat transfer. A new correlation for the stagnation line heat transfer has been developed that includes the spanwise fluctuating vorticity components.

Measurement and Prediction of Heat Transfer Distributions on an Aft Loaded Vane Subjected to the Influence of Catalytic and Dry Low NOx Combustor Turbulence

2003 ◽  
Author(s):  
F. E. Ames ◽  
M. Argenziano ◽  
C. Wang
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Energy Scale ◽  
Test Case ◽  
Suction Surface ◽  
Stagnation Region ◽  
Data Set ◽  
Transfer Rates ◽  
Pressure Surface ◽  
Heat Transfer Augmentation

This paper documents heat transfer rates on an aft loaded vane subject to turbulence generated by mock combustion configurations representative of recently developed catalytic and dry low NOx (DLN) combustors. New combustion systems developed for low emissions have produced substantial changes to the characteristics of inlet turbulence entering nozzle guide vanes. Aft loaded vane designs can have an impact on surface heat transfer distributions by accelerating boundary layers for a greater portion of the suction surface. Four different inlet turbulence conditions with intensities ranging up to 21 percent are documented in this study and vane heat transfer rates are acquired at vane exit chord Reynolds numbers ranging from 500,000 to 2,000,000. Heat transfer distributions show the influence of the turbulence conditions on heat transfer augmentation and transition. Cascade aerodynamics are well documented and match pressure distributions predicted by a commercial CFD code for this large scale low speed facility. The aft loaded vane pressure distribution exhibits a minimum value at about 50 percent arc on the suction surface. Laminar heat transfer augmentation in the stagnation region and on the pressure surface have scaled well on theoretical parameters based on turbulence intensity, Reynolds number, and energy scale. Predictive comparisons are shown based on a two-dimensional boundary layer code using an algebraic turbulence model for augmentation as well as a transition model. This comprehensive vane heat transfer data set is expected to represent an excellent test case for vane heat transfer predictive methods.

scholarly journals Experimental Heat Transfer Distributions Over an Aft Loaded Vane With a Large Leading Edge at Very High Turbulence Levels

2016 ◽  
Author(s):  
Justin W. Varty ◽  
Forrest E. Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Constant Heat Flux ◽  
Test Surface ◽  
Stagnation Region ◽  
Experimental Heat ◽  
High Turbulence ◽  
Very High

Vane heat transfer distributions have been acquired on an aft loaded vane with a large leading edge over a range of turbulence conditions and across a range of Reynolds numbers. The large leading edge was designed to reduce heat transfer levels around the vane stagnation region and provide an opportunity to internally cool the region using a double wall cooling method. Heat transfer measurements were acquired in a linear cascade using a constant heat flux technique. The cascade was designed in a four vane, three full passage configuration with inlet bleeds flows and exit tailboards shaped along streamlines. Heat transfer measurements were acquired at exit chord Reynolds numbers of 500,000, 1,000,000, and 2,000,000 over seven turbulence conditions. The turbulence conditions included a low turbulence condition (Tu ≈ 0.7%), a small grid (M = 3.175 cm) at far and near locations (Tu ≈ 3.5% & 7.9%), a larger grid (Tu ≈ 8.0%), an aero-combustor closely coupled to the cascade and with a decay spool in between (Tu ≈ 13.5% and 9.3%) as well as with a new very high turbulence generator (Tu ≈ 17.4%). Heat transfer levels in the stagnation region are correlated in terms of approach flow Reynolds number and turbulence conditions and compared with recent large cylindrical leading edge test surface data using the TRL parameter. The surface heat transfer measurements are presented at different Reynolds numbers in terms of Stanton number based on exit conditions. These comparisons provide useful information on the level of turbulence augmentation in laminar regions of the flow as well as the onset location and length of transition. Midspan surface static pressure distributions were acquired at all the conditions and were used as a basis to determine experimental isentropic Mach number distributions. These data are reported in part but were also used to help generate the free-stream boundary condition for a boundary layer calculation. Predictive comparisons generated from boundary layer calculations (STAN7) using an algebraic turbulence model (ATM) and a well-known transition model (Mayle) are provided. At low turbulence levels the close comparisons provide confidence in the experimental technique. At higher turbulence levels the comparisons may provide a better indication of the physics of response of vane heat transfer to the external turbulence. These data are expected to help clarify the physics of vane heat transfer at very high turbulence levels.

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