Heat Transfer Enhancement by Criss-Cross Pattern Formed by 45° Angled Rib Turbulators in a Straight Square Duct

2017 ◽  
Author(s):  
Prashant Singh ◽  
Yongbin Ji ◽  
Mingyang Zhang ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Hydraulic Performance ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Conduction Model ◽  
Square Duct ◽  
Rib Turbulators

The need for higher turbine efficiency has been constantly pushing the turbine inlet temperatures to elevated levels. Hot gas path temperatures are much higher than the typical blade material yield temperature. Efficient internal cooling technologies are required for safe operation of gas turbine. Several internal cooling technologies have been developed in order to enhance the heat transfer from relatively hotter walls of turbine blade. For mid-chord region of turbine blade, rib turbulators are typically installed in multi-pass channels. Rib turbulators trip the boundary layer, induce secondary flows which enhance near wall shear as well as enhance turbulent mixing when they interact with surrounding walls. Research has been carried out on several aspects of rib turbulated passages in order to achieve higher thermal hydraulic performance. Generally, rib turbulators are installed on two opposite walls of serpentine passages in order to enhance heat transfer from both pressure and suction sides of blade through coolant flowing through complicated paths. Typical arrangement of rib turbulators were parallel to each other or having some offset from each other. In the present study, an attempt has been made to arrange 45° angled ribs in a way that they form a Criss-Cross pattern. Two ribbed configurations with Criss-Cross pattern - Inline and staggered, have been studied where the baseline case was smooth duct with no rib turbulators. The effective rib-pitch-to-rib-height ratio (p/e) was 8.6 and rib-height-to-channel-hydraulic diameter ratio (e/dh) was 0.1. The channel had a total length of 20 hydraulic diameters and the rib turbulators were installed at a distance of six hydraulic diameters from the inlet of the test section to allow flow development. Detailed heat transfer coefficients were measured using transient liquid crystal thermography employing 1D semi-infinite conduction model. Globally averaged Nusselt numbers are calculated from the detailed measurements and thermal hydraulic performance of configurations have been reported with respect to Reynolds number. The aim of this study was to develop a cooling configuration which has higher thermal-hydraulic performance compared to other traditional rib configurations. It has been found that the heat transfer characteristics of the inline and staggered configurations were similar to each other and ranged between three times D-B correlation to 2.7 times, for Reynolds number ranging from 30000 to 60000. Inline configuration had relatively lower frictional losses, however the thermal hydraulic performances of both the configurations were similar.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring a Converging Tip Turn With Various 45 deg Rib Coverage Designs

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Copper Plate ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
First Passage ◽  
Pressure Loss Coefficient ◽  
Internal Surfaces ◽  
Turbine Airfoils

Varying aspect ratio (AR) channels are found in modern gas turbine airfoils for internal cooling purposes. Corresponding experimental data are needed in understanding and assisting the design of advanced cooling systems. The present study features a two-pass rectangular channel with an AR = 4:1 in the first pass with the radial outward flow and an AR = 2:1 in the second pass with the radial inward flow after a 180 deg tip turn. Effects of rib coverage near the tip region are investigated using profiled 45 deg ribs (P/e = 10, e/Dh ≈ 0.11, parallel and in-line) with three different configurations: less coverage, medium coverage, and full coverage. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage. The highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Heat transfer coefficients on the internal surfaces were obtained by the regionally averaged copper plate method. The results showed that the rotation effects on both heat transfer and pressure loss coefficient are reduced with an increased rib coverage in the tip turn region. Different rib coverage upstream of the tip turn significantly changes the heat transfer in the turn portion. Heat transfer reduction (up to −27%) on the tip wall was seen at lower Ro. Dependence on the Reynolds number can be seen for this particular design. The combined geometric, rib coverage, and rotation effects should be taken into consideration in the internal cooling design.

scholarly journals Effect of Reynolds Number and Property Variation on Fluid Flow and Heat Transfer in the Entrance Region of a Turbine Blade Internal-Cooling Channel

2005 ◽  
Vol 2005 (1) ◽  
pp. 36-44 ◽  
Author(s):  
R. Ben-Mansour ◽  
L. Al-Hadhrami
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mass Flow Rate ◽  
Heat Transfer Rate ◽  
Turbine Blade ◽  
Flow Rate ◽  
Transfer Rate ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Flow And Heat Transfer

Internal cooling is one of the effective techniques to cool turbine blades from inside. This internal cooling is achieved by pumping a relatively cold fluid through the internal-cooling channels. These channels are fed through short channels placed at the root of the turbine blade, usually called entrance region channels. The entrance region at the root of the turbine blade usually has a different geometry than the internal-cooling channel of the blade. This study investigates numerically the fluid flow and heat transfer in one-pass smooth isothermally heated channel using the RNGk−εmodel. The effect of Reynolds number on the flow and heat transfer characteristics has been studied for two mass flow rate ratios (1/1and1/2) for the same cooling channel. The Reynolds number was varied between10 000and50 000. The study has shown that the cooling channel goes through hydrodynamic and thermal development which necessitates a detailed flow and heat transfer study to evaluate the pressure drop and heat transfer rates. For the case of unbalanced mass flow rate ratio, a maximum difference of8.9% in the heat transfer rate between the top and bottom surfaces occurs atRe=10 000while the total heat transfer rate from both surfaces is the same for the balanced mass flow rate case. The effect of temperature-dependent property variation showed a small change in the heat transfer rates when all properties were allowed to vary with temperature. However, individual effects can be significant such as the effect of density variation, which resulted in as much as9.6% reduction in the heat transfer rate.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (Aspect Ratio = 4:1 to 2:1) With Profiled 60 deg Angled Ribs

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
First Passage ◽  
Cross Sectional ◽  
Internal Surfaces

The present study features a two-pass rectangular channel with an aspect ratio (AR) = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180-deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ∼ 0.11, parallel and in-line). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all internal surfaces. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. The results showed that the turn-induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction (∼30%) on the tip wall was seen in both the smooth and ribbed cases under rotating condition. Overall pressure penalty was reduced for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

Optimization of Rib Shape and Inclination in a Square Duct with Response Surface Methodology

2021 ◽  
pp. 1-34
Author(s):  
Yigang Luan ◽  
Lanyi Yan ◽  
Yue Yin ◽  
Hao Fu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Response Surface ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Square Duct ◽  
Flow And Heat Transfer ◽  
Surface Method ◽  
Geometric Factors ◽  
Parameter Ranges

Abstract The paper conducts numerical investigation coupled with Reynolds-averaged Navier Stokes method on detailed flow field and heat transfer characteristics of ribbed channel with symmetric ribs mounted on two walls. The physical domain is modeled by reference to a practical turbine blade internal cooling channel. The effects of three selected geometric factors of ribs, i.e. rib inclination angle, dimensionless rib height and dimensionless rib pitch, on the flow and heat transfer are investigated by variable-controlled simulations with the Reynolds number ranges from 5,000 to 90,000. The parameter ranges are 30°≤a≤90°, 0.5≤e/w≤1.5 and 5≤P/w≤15 with the rib width w fixed at 1mm. It is newly found that the friction factor does not follow a monotonical trend with respect to the Reynolds number under certain rib configurations. In addition, three-level numerical calculations about three geometric factors as well as the Reynolds number are conducted with the response surface method (RSM). Quadratic regression model for the targeted response, TPF, is obtained. The optimal rib shape for the goal of maximizing the channel overall thermal performance turns out to be e/w=0.5, P/w=15, a=30° as Re is fixed at 30,000.

Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs of Various Angles

2002 ◽  
Author(s):  
Rongguang Jia ◽  
Arash Saidi ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Experimental Studies ◽  
Eddy Diffusivity ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients

Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000–30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.

Regional Heat Transfer and Pressure Drop in Two-Pass and Three-Pass Flow Passages With 180-Degree Sharp Turns

1989 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient ◽  
Single Turn

The heat transfer distributions for flow passing through a two-pass (one-turn) and a three-pass (two-turn) passages with 180-degree sharp turns are studied by using the analogous naphthalene mass transfer technique. Both passages have square cross-section and length-to-height ratio of 8. The passage surface, including top wall, side walls and partition walls, is divided into 26 segments for the two-pass passage and 40 segments for the three-pass passage. Mass transfer results are presented for each segment along with regional and overall averages. The very non-uniform mass transfer coefficients measured around a sharp 180-degree turn exhibit the effects of flow separation, reattachment and impingement, in addition to secondary flows. Results of the three-pass passage indicate that heat transfer characteristics around the second turn is virtually the same as that around the first turn. This may imply that, in a multiple-pass passage, heat transfer at the first turn has already reached the thermally developed (periodic) condition. Over the entire two-pass passage, the heat transfer enhancement induced by the single-turn is about 45% to 65% of the fully developed values in a straight channel. Such a heat transfer enhancement decreases with an increase in Reynolds number. In addition, overall heat transfer of the three-pass passage is approximately 15% higher than that of the two-pass one. This 15% increase appears to be Reynolds number independent. The pressure loss induced by the sharp turns is found to be very significant. Within the present testing range, the pressure loss coefficient for both passages varies significantly with the Reynolds number.

Heat Transfer and Pressure Drop in a Rotating Two-Pass Square Channel With Different Ribs at High Rotation Numbers

2015 ◽  
Author(s):  
Yang Li ◽  
Hongwu Deng ◽  
Guoqiang Xu ◽  
Shuqing Tian
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Flow Direction ◽  
Moderate Pressure ◽  
Transfer Coefficients ◽  
Square Channel ◽  
Smooth Case ◽  
Rib Turbulators

Rotation effects on heat transfer and pressure drop in a rotating two-pass square channel with ribs is experimentally investigated. The cooper plate heating technique is applied to obtain the regional average heat transfer coefficients. The Reynolds number and rotation number varies from 10000 to 60000, and 0 to 2.0, respectively. Rib turbulators are placed on the leading and trailing walls of the channel at an angle of 90 deg or 45 deg to the flow direction. The rib pitch-to-height (P/e) ratio is 10 and the height-to-hydraulic diameter (e/Dh) ratio is 0.1 for all tests. The detailed comparisons between smooth wall case and ribbed wall cases are presented. At stationary, increasing the Reynolds number decreases heat transfer and thermal performance ratios, but raises the friction factor ratios dramatically. Rotation shows the strongest effect on heat transfer in smooth case, and then 90 deg rib case, and the least in 45 deg rib case. Channel friction in smooth case is increased by rotation monotonously, but decreases with Ro in ribbed case when Ro increases up to 0.5. The similar thermal performances trends are observed for smooth and ribbed cases at rotation but with different peak point. The 45 deg rib channel has the superior thermal performance because it incurs the highest heat transfer and moderate pressure penalty.

Influence of Unsteady Wake on Heat Transfer Coefficient From a Gas Turbine Blade

1993 ◽  
Vol 115 (4) ◽  
pp. 904-911 ◽  
Author(s):  
J.-C. Han ◽  
L. Zhang ◽  
S. Ou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbine ◽  
Strouhal Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Unsteady Wake ◽  
Wake Passing

The effect of unsteady wake on surface heat transfer coefficients of a gas turbine blade was experimentally determined using a spoked wheel type wake generator. The experiments were performed with a five-airfoil linear cascade in a low-speed wind tunnel facility. The cascade inlet Reynolds number based on the blade chord was varied from 1 to 3 × 105. The wake Strouhal number was varied between 0 and 1.6 by changing the rotating wake passing frequency (rod speed and rod number), rod diameter, and cascade inlet velocity. A hot-wire anemometer system was located at the cascade inlet to detect the instantaneous velocity, phase-averaged mean velocity, and turbulence intensity induced by the passing wake. A thin foil thermocouple instrumented blade was used to determine the surface heat transfer coefficients. The results show that the unsteady passing wake promotes earlier and broader boundary layer transition and causes much higher heat transfer coefficients on the suction surface, whereas the passing wake also significantly enhances heat transfer coefficients on the pressure surface. The blade heat transfer coefficients for a given Reynolds number flow increase with the wake Strouhal number by increasing the rod speed, rod number, or rod diameter. For a given wake passing frequency and rod diameter, the blade heat transfer coefficients decrease with decreasing Reynolds number, although the corresponding wake Strouhal number is increased. The results suggest that both the Reynolds and Strouhal numbers are important parameters in determining the blade heat transfer coefficients in unsteady wake flow conditions.

Detailed Heat Transfer Coefficient Measurements on a Scaled Realistic Turbine Blade Internal Cooling System

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Chao-Cheng Shiau ◽  
Andrew F. Chen ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Cooling System ◽  
Plastic Material ◽  
Local Heat Transfer ◽  
Transfer Characteristic ◽  
Internal Cooling ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Trailing Edge

Abstract A realistic internal cooling system of a turbine blade includes both ribs and pin-fins inside the passages to enhance the heat transfer. However, the majority studies in the open literature assessing the heat transfer characteristics on a simplified cooling model by examining ribbed-roughen passages and pin-finned passage separately. This work presents the high-resolution heat transfer coefficients of a scaled realistic turbine blade internal cooling design. The cooling system, using a 3D-printed plastic material, consists of an S-shaped inlet, four serpentine passages (three U-bends) of variable aspect ratio, and the trailing edge ejection. Angled ribs are implemented inside the passages and the elongated fins and pins are used near the trailing edge. Two dust holes are realized on the blade tip, the injections are individually controlled to reflect the realistic coolant flowrate variation inside the entire internal cooling system. The tests are conducted at two Reynolds number, 45,000 and 60,000 based on the hydraulic diameter of the inlet passage. Transient heat transfer technique using thermochromic liquid crystal is applied to obtain the detailed heat transfer characteristic inside the cooling channel. The local and averaged Nusselt numbers are also compared with the correlations in the open literature. This paper provides gas turbine designers the difference of local heat transfer distributions between the realistic and simplified internal cooling designs.

Average Nusselt Number for Pressure and Suction Sides of Squealer Turbine Blade Tip

2011 ◽  
Author(s):  
Chaouki Ghenai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Blade Tip

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

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