Numerical Investigation of Convective Heat Transfer and Pressure Drop for Ribbed Surfaces in the Bend Part of a U-Duct

2012 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Pressure Coefficient ◽  
Turbine Blades ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Gas Turbine Blades ◽  
Cross Section Area ◽  
Duct Geometry ◽  
Energy Equations

This work concerns two-dimensional numerical simulations of the flow and temperature fields inside smooth and ribbed bend (turn) parts of a U-duct with relevance for internal tip cooling of gas turbine blades. The ribs are placed internally on the outermost bend surface. The renormalization group (RNG) k-ε turbulence model was used to solve the momentum and energy equations inside the bend (turn) part as well in the supply and return straight parts of the U-duct. For the ribbed surface three different rib configurations were simulated, namely (a) single rib at three different rib positions, i.e., inlet, middle and outlet, (b) two ribs for three different configurations, i.e., at the inlet and middle, at the middle and outlet as well as at the inlet and outlet, and (c) three ribs. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1, the pitch ratios were 13.5 and 27 and the Reynolds number was 20000. The details of the duct geometry were as follows: the cross section area of the straight part was 50×50 mm2, the inside length of the bend part was 240 mm. The results were compared with experimental data obtained at similar conditions. The numerical results were closer to the experimental ones for those cases with the rib at the inlet position than for the cases with the rib at the middle position. The case of two ribs at the inlet and middle gave the highest heat transfer coefficients while the case of a single rib at the middle gave the highest local pressure coefficient of all cases.

Laminar and Transitional Boundary Layer Structures in Accelerating Flow With Heat Transfer

1986 ◽  
Vol 108 (1) ◽  
pp. 116-123 ◽  
Author(s):  
K. Rued ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Pressure Gradients ◽  
Transfer Coefficients ◽  
Gas Turbine Blades ◽  
Heat Transfer Coefficients ◽  
Layer Structures ◽  
Flow Heat

The accurate prediction of heat transfer coefficients on cooled gas turbine blades requires consideration of various influence parameters. The present study continues previous work with special efforts to determine the separate effects of each of several parameters important in turbine flow. Heat transfer and boundary layer measurements were performed along a cooled flat plate with various freestream turbulence levels (Tu = 1.6−11 percent), pressure gradients (k = 0−6 × 10−6), and cooling intensities (Tw/T∞ = 1.0−0.53). Whereas the majority of previously available results were obtained from adiabatic or only slightly heated surfaces, the present study is directed mainly toward application on highly cooled surfaces as found in gas turbine engines.

Comparison of Continuous and Truncated Ribs on Internal Blade Tip Cooling

2012 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbine Blades ◽  
Ccd Camera ◽  
Outer Wall ◽  
Transfer Coefficients ◽  
Duct Geometry ◽  
Blade Tip ◽  
Cooling Passage ◽  
Cooling Air

In the present work, an experimental study related to turbulent flow inside the bend part of a U-duct geometry was performed concerning pressure drop and heat transfer. Such duct geometries can be found inside gas turbine blades, where the cooling air extracts heat from hot internal walls while it is flowing inside the cooling passage. Both friction factors and convective heat transfer coefficients were established inside the bend part of the U-duct for two different rib cases, namely continuous and truncated ribs with varying Reynolds number from 8,000 to 20,000. For the continuous rib case, the length of the ribs was equal to the height of the duct while in the truncated rib case two different rib lengths, i.e., 46 mm and 40 mm, respectively, were considered. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1 and the pitch ratio was 10. The test rig has been built in such a way that various experimental setups can be handled as the outer wall of the bend (turn) part of the U-duct can easily be removed and the ribs can be changed. Both the U-duct and the ribs were made from acrylic material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on the narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The ribs were placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The pressure drop was almost identical for the continuous and truncated rib cases, while the heat transfer coefficient is 10% higher for the continuous rib case at Re = 20000. The uncertainties in the evaluated properties were 3% and 6% for the Nusselt number and friction factor, respectively.

Calculation of Heat Transfer Coefficients in Cooled Turbine Cascades

1966 ◽  
Vol 17 (3) ◽  
pp. 253-268 ◽  
Author(s):  
H. D. Harris ◽  
R. E. Luxton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Turbine Blades ◽  
Order Estimate ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Heat Transfer Coefficients ◽  
Blade Cooling

SummaryAn approximate method is presented for the calculation of heat transfer rates to cooled turbine blades. The method is based on a combination and extension of methods which have been developed in recent years for the calculation of the skin friction and heat transfer coefficients on wings in high speed flight. The use of the method is demonstrated by application to a specific cascade for which an experimental determination of overall heat transfer coefficient is known. Very close agreement with the experimental results is found over the range of Reynolds number tested. The calculated distribution of local heat transfer coefficient indicates that local pressure gradients have a marked effect on the heat transfer. A first-order estimate of the effect of blade cooling on the rate of mass flow through a blade passage shows that an increase of the order of one per cent in the mass flow rate may be obtained by a reasonable degree of blade cooling.

Calculation of Heat Transfer to Convection-Cooled Gas Turbine Blades

1985 ◽  
Vol 107 (3) ◽  
pp. 620-627 ◽  
Author(s):  
W. Rodi ◽  
G. Scheuerer
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Complex Nature ◽  
Surface Boundary ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Gas Turbine Blades ◽  
Heat Transfer Coefficients

A mathematical model is presented for calculating the external heat transfer coefficients around gas turbine blades. The model is based on a finite-difference procedure for solving the boundary-layer equations which describe the flow and temperature field around the blades. The effects of turbulence are simulated by a low-Reynolds number version of the k-ε turbulence model. This allows calculation of laminar and transitional zones and also the onset of transition. Applications of the calculation method are presented to turbine-blade situations which have recently been investigated experimentally. Predicted and measured heat transfer coefficients are compared and good agreement with the data is observed. This is true especially for the pressure-surface boundary layer which is of a rather complex nature because it remains in a transitional state over the full blade length. The influence of various flow phenomena like laminar-turbulent transition and of the boundary conditions (pressure gradient, free-stream turbulence) on the predicted heat transfer rates is discussed.

scholarly journals Turbulent Flow and Heat Transfer in Gas Turbine Blade Cooling Passages

1992 ◽  
Author(s):  
F. J. Cunha
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Air Cooling ◽  
Turbine Blade Cooling ◽  
Gas Turbine Blades ◽  
Analysis Methodology

A numerical analysis methodology has been created to predict the heat transfer within the air cooling passages of gas turbine blades. In this paper, the turbulent flow heat convection with developed velocity and temperature fields is studied for cavities with turbulators. The influence of Coriolis forces and rotational buoyancy effects were also included. The k-equation turbulence model was employed over most of the cross section while a modified Van Driest’s version of the mixing length hypothesis is used in the near-wall sublayer. This methodology was successfully benchmarked against experimental results for air cooling passages of turbine blades. Analytical results are presented in terms of the Reynolds, Rossby and rotational Rayleigh numbers for realistic operating conditions.

scholarly journals High Reynold Number LES of a Rotating Two-Pass Ribbed Duct

Aerospace ◽  
2018 ◽  
Vol 5 (4) ◽  
pp. 124 ◽  
Author(s):  
Danesh Tafti ◽  
Cody Dowd ◽  
Xiaoming Tan
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Turbine Blades ◽  
Computational Cost ◽  
Reynold Number ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
Gas Turbine Blades ◽  
Eddy Simulation ◽  
Turbulent Statistics

Cooling of gas turbine blades is critical to long term durability. Accurate prediction of blade metal temperature is a key component in the design of the cooling system. In this design space, spatial distribution of heat transfer coefficients plays a significant role. Large-Eddy Simulation (LES) has been shown to be a robust method for predicting heat transfer. Because of the high computational cost of LES as Reynolds number (Re) increases, most investigations have been performed at low Re of O(104). In this paper, a two-pass duct with a 180° turn is simulated at Re = 100,000 for a stationary and a rotating duct at Ro = 0.2 and Bo = 0.5. The predicted mean and turbulent statistics compare well with experiments in the highly turbulent flow. Rotation-induced secondary flows have a large effect on heat transfer in the first pass. In the second pass, high turbulence intensities exiting the bend dominate heat transfer. Turbulent intensities are highest with the inclusion of centrifugal buoyancy and increase heat transfer. Centrifugal buoyancy increases the duct averaged heat transfer by 10% over a stationary duct while also reducing friction by 10% due to centrifugal pumping.

Aerodynamic Performance of Porous Gas Turbine Blades

1969 ◽  
Vol 73 (705) ◽  
pp. 789-796 ◽  
Author(s):  
F. J. Bayley ◽  
G. R. Wood
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
High Heat ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Gas Turbine Blades ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Aero Engines ◽  
Cooling Air

If maximum gas temperatures aire to rise appreciably above 1500°K, the value currently achieved in advanced aero-engines, alternatives to the present internal convective methods of air-cooling the first-stage turbine blades will have to be sought. One of the most promising developments lies in the use of porous blade materials, through which cooling air can be “effused” or “transpired”. In a recent paper Bayley and Turner have shown that by the combination of high heat transfer coefficients within the interstices of the porous material, and a reduction in heat transfer rate by injection into the boundary layer on the hot-gas side of the blade, effective cooling rates can be achieved.

Determination of Heat Transfer Coefficients Around a Blade Surface From Temperature Measurements

1979 ◽  
Author(s):  
D. K. Mukherjee
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Main Stream ◽  
Blade Surface ◽  
Transfer Coefficients ◽  
Gas Turbine Blades ◽  
Heat Transfer Coefficients

To design cooled gas turbine blades, heat transfer coefficients around its surface are required. The calculated heat transfer data under operating conditions in the turbine are often inaccurate and require experimental verification. A method is presented here to determine the heat transfer coefficients around the blade surface and in the coolant channels. This requires measurements of the main stream and coolant temperatures together with the outer surface temperature distribution at varying mass flows. In order to conduct these tests in a gas turbine, test blades have to be specially prepared allowing the variation and measurement of coolant mass flow.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

Sign in / Sign up

Export Citation Format

Share Document