Effects of Unsteady Wakes on Heat Transfer of Blade Tip and Shroud

2017 ◽  
Author(s):  
Minho Bang ◽  
Seok Min Choi ◽  
Ho-Seong Sohn ◽  
Jun Su Park ◽  
Hyung Hee Cho
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Swirling Flow ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Blade Tip ◽  
Flow Reattachment ◽  
Blade Tips

An experimental study has been conducted to investigate the heat-transfer characteristics of blade tips and shrouds with and without unsteady wakes. Depending on the presence of unsteady wakes, the local heat/mass-transfer coefficients of the tip and shroud were measured using the naphthalene sublimation method. Wakes from unsteady blades were modeled as wakes generated from moving cylindrical rod bundles. Test conditions were set to the Reynolds number of 100,000, based on an inlet velocity of 11.4 m/s and the axial chord length. The Strouhal number was varied from 0 to 0.22. For St = 0, high heat/mass-transfer coefficients appeared in regions where various flow patterns, such as flow reattachment, swirling flow, and vortexes, occurred. For St = 0.22, the heat/mass-transfer distributions of the tip and shroud were changed due to the unsteady wakes. Unsteady wakes made high turbulence intensity of leakage flow and flow patterns such as flow reattachment, swirling flow, and tip leakage vortex in the tip and shroud were changed and dispersed. There were also variations in the pitch-wise averaged Sherwood number of the blade tip and shroud on the presence of the unsteady wakes due to vortex shedding and dispersed flow patterns. Thus, considering the effects of unsteady wakes on the heat transfer of the blade tip and shroud, proper cooling designs for blade tips and shrouds should be investigated and adopted for effective cooling of gas turbine blades.

Heat Transfer in Wavy Duct With Different Corrugation Angle

2002 ◽  
Author(s):  
Sang Dong Hwang ◽  
Han Ho Kim ◽  
Hyung Hee Cho ◽  
Seung Bae Chen
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Side Wall ◽  
Pressure Side ◽  
Secondary Vortex ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Flow Cells ◽  
Sharp Turn

The present study investigates the effects of duct corrugation angle and flow velocity on the convective heat/mass transfer characteristics in wavy ducts applied in a primary surface heat exchanger. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The flow visualization technique is used to understand the overall flow structures inside the duct. The corrugation angles of the wavy ducts are 145° and 130°, and the duct aspect ratio is fixed at 7.3. The Reynolds numbers, based on the duct hydraulic diameter, vary from 1,000 to 5,000. The results show that secondary vortex flow cells, called Taylor-Go¨rtler vortices, exist periodically in the wavy duct. Therefore, non-uniform distributions of the heat/mass transfer coefficients are obtained on the duct walls. On the pressure-side wall, high heat/mass transfer cell-shaped regions appear due to the secondary vortex flows for both corrugation angles. On the suction-side wall, the heat transfer coefficients are lower than those on the pressure-side wall. The wavy duct with the corrugation angle of 130° has the stronger strength of the secondary vortex cells resulting in higher heat/mass transfer rates on the duct wall because the sharp turn enhances the development of the secondary flow cells.

Effect of Blade Tip Clearance on Turbine Shroud Heat/Mass Transfer

2001 ◽  
Author(s):  
Dong Ho Rhee ◽  
Jong Hyun Choi ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Large Scale ◽  
Local Heat ◽  
Tip Clearance ◽  
Pressure Side ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Transfer Characteristics ◽  
Blade Tip

This study investigates the local heat/mass transfer characteristics on the stationary shroud with blade tip clearances for flat tip geometry. A large scale linear cascade is used and the relative motion between the blade and shroud is neglected in this study. A naphthalene sublimation method is employed to determine the detailed local heat/mass transfer coefficients on the shroud surface. The geometry of blade tip used in this study is flat and the tip clearance varies from 0.66% to 2.85% of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the pressure difference. Therefore, the heat/mass transfer characteristics on the shroud are changed significantly from those for no tip clearance. High heat/mass transfer region is observed along the pressure side of blade due to the entrance effect and the acceleration of the tip gap flow. Complex heat transfer patterns on the shroud are observed in the region where the blade tip and shroud are overlapped due to the flow separation and reattachment. Then, the heat/mass transfer coefficients on the shroud increase along the suction side of blade because tip leakage vortices are generated with interacting the main flow. The experimental results show that the heat/mass transfer characteristics are changed significantly with the gap distance between the tip of turbine blade and the shroud. However, the turbulence intensity of incoming flow has little influence on the heat/mass transfer coefficients on the shroud with tip clearance.

Influence of Injection Type and Feed Arrangement on Flow and Heat Transfer in an Injection Slot

2001 ◽  
Vol 124 (1) ◽  
pp. 132-141 ◽  
Author(s):  
Hyung Hee Cho ◽  
Jin Ki Ham
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Cooling System ◽  
Transfer Coefficients ◽  
Counter Flow ◽  
Flow Paths ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Vertical Injection ◽  
Injection Type

An experimental investigation is conducted to improve a slot film cooling system used for the cooling of a gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal, inline, and counter-flow paths to the mainstream flow direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot wall with various injection types and coolant feeding directions. A numerical simulation is also conducted to help understand the flow patterns inside the slot for different injection types. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the injection hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The dimensionless temperature distributions at the slot exits differ little with blowing rates, injection types, and secondary flow conditions. In the results of heat/mass transfer measurements, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effects of jet impingement. The lateral distributions of heat/mass transfer coefficients with the inline and counter-flow paths are more uniform than the normal-flow path. The average heat/mass transfer coefficients with the injection holes are about two to five times higher than that of a smooth two-dimensional slot path.

scholarly journals Highly Resolved Distribution of Heat Transfer for Turbine Leading Edge Film Cooling Including Reynolds Number and Blowing Rate Effects

1998 ◽  
Author(s):  
K. Jung ◽  
D. K. Hennecke
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Leading Edge ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Long Distance ◽  
Naphthalene Sublimation Technique

The effect of leading edge film cooling on heat transfer was experimentally investigated using the naphthalene sublimation technique. The experiments were performed on a symmetrical model of the leading edge suction side region of a high pressure turbine blade with one row of film cooling holes on each side. Two different lateral inclinations of the injection holes were studied: 0° and 45°. In order to build a data base for the validation and improvement of numerical computations, highly resolved distributions of the heat/mass transfer coefficients were measured. Reynolds numbers (based on hole diameter) were varied from 4000 to 8000 and blowing rate from 0.0 to 1.5. For better interpretation, the results were compared with injection-flow visualizations. Increasing the blowing rate causes more interaction between the jets and the mainstream, which creates higher jet turbulence at the exit of the holes resulting in a higher relative heat transfer. This increase remains constant over quite a long distance dependent on the Reynolds number. Increasing the Reynolds number keeps the jets closer to the wall resulting in higher relative heat transfer. The highly resolved heat/mass transfer distribution shows the influence of the complex flow field in the near hole region on the heat transfer values along the surface.

Local Heat/Mass Transfer Characteristics on a Rotating Blade With Flat Tip in a Low-Speed Annular Cascade—Part II: Tip and Shroud

2005 ◽  
Vol 128 (1) ◽  
pp. 110-119 ◽  
Author(s):  
Dong-Ho Rhee ◽  
Hyung Hee Cho
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Flow Velocity ◽  
Rotational Speed ◽  
Heat Mass Transfer ◽  
Local Heat ◽  
Incoming Flow ◽  
Transfer Coefficients ◽  
Low Speed ◽  
Annular Cascade

The local heat/mass transfer characteristics on the tip and shroud were investigated using a low speed rotating turbine annular cascade. Time-averaged mass transfer coefficients on the tip and shroud were measured using a naphthalene sublimation technique. A low speed wind tunnel with a single stage turbine annular cascade was used. The turbine stage is composed of sixteen guide plates and blades. The chord length of blade is 150 mm and the mean tip clearance is about 2.5% of the blade chord. The tested Reynolds number based on inlet flow velocity and blade chord is 1.5×105 and the rotational speed of the blade is 255.8 rpm at design condition. The results were compared with the results for a stationary blade and the effects of incidence angle of incoming flow were examined for incidence angles ranging from −15 to +7deg. The off-design test conditions are obtained by changing the rotational speed with a fixed incoming flow velocity. Flow reattachment on the tip near the pressure side edge dominates the heat transfer on the tip surface. Consequently, the heat/mass transfer coefficients on the blade tip are about 1.7 times as high as those on the blade surface and the shroud. However, the heat transfer on the tip is about 10% lower than that for the stationary case due to reduced leakage flow with the relative motion. The peak regions due to the flow reattachment are reduced and shifted toward the trailing edge and additional peaks are formed near the leading edge region with decreasing incidence angles. But, quite uniform and high values are observed on the tip with positive incidence angles. The time-averaged heat/mass transfer on the shroud surface has a level similar to that of the stationary cases.

Effects of Fin Shapes and Arrangements on Heat Transfer for Impingement/Effusion Cooling With Crossflow

2005 ◽  
Author(s):  
Sung Kook Hong ◽  
Dong-Ho Rhee ◽  
Hyung Hee Cho
Keyword(s):  
Mass Transfer ◽  
Heat Mass Transfer ◽  
Flow Characteristics ◽  
Local Heat ◽  
Wall Jet ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Blowing Ratio ◽  
Transfer Characteristics ◽  
Sublimation Method

The present paper has investigated the effects of fin on the flow and heat/mass transfer characteristics for the impingement/effusion cooling with crossflow. The fins of circular or rectangular shape are installed between two perforated plates and the crossflow passes between these two plates. The blowing ratio is changed from 0.5 to 1.5 for a fixed jet Reynolds number of 10,000. A naphthalene sublimation method is used to obtain the local heat/mass transfer coefficients on the effusion plate. A numerical calculation is also performed to investigate the flow characteristics. Flow and heat/mass transfer characteristics are changed significantly due to installation of fins. In the injection region, wall jet spreads more widely than the case without fins because fin prevents the wall jet from being swept away by the crossflow. In the effusion region, higher heat/mass transfer coefficient is obtained due to the flow disturbance and acceleration by the fin. As the blowing ratio increases, the effects of fin against the crossflow become more significant and then the higher average heat/mass transfer coefficients are obtained. Especially, the cases with rectangular fins have about 40%∼45% enhancement at the high blowing ratio of M = 1.5. However, the increase of blockage effect gives more pressure loss in the channel.

Performance of One- and Two-Row Tube and Plate Fin Heat Exchangers

1984 ◽  
Vol 106 (3) ◽  
pp. 627-632 ◽  
Author(s):  
E. C. Rosman ◽  
P. Carajilescov ◽  
F. E. M. Saboya
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Exchangers ◽  
Local Heat Transfer ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Fin Efficiency ◽  
Heat Transfer Coefficients ◽  
Experimental Apparatus

Heat exchangers consisting of finned tubes are commonly employed in air conditioning systems, air heaters, radiators, etc. Local measurements of mass transfer coefficients on fins, obtained by Saboya and Sparrow, are very nonuniform. In the present work, an experimental apparatus was set up to measure overall heat transfer coefficients for two-row tube and plate fin heat exchangers. The obtained results, together with Shepherd’s results for one-row exchangers, are used to transform the local mass transfer coefficients into local heat transfer coefficients. A numerical two-dimensional heat transfer analysis has been performed in order to obtain the temperature distribution and fin efficiency. The influences of the Reynolds number and fin material are also analyzed.

Heat Transfer Characteristics of an Obliquely Impinging Circular Jet

1980 ◽  
Vol 102 (2) ◽  
pp. 202-209 ◽  
Author(s):  
E. M. Sparrow ◽  
B. J. Lovell
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Local Heat ◽  
Maximum Point ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Naphthalene Sublimation Technique ◽  
Local Coefficients ◽  
Naphthalene Sublimation

Measurements of local heat (mass) transfer coefficients were made on a surface on which a circular jet impinges at an oblique angle. The angle of inclination of the jet relative to the surface was varied from 90 deg (normal impingement) to 30 deg. The Reynolds number and the distance between the jet orifice and the impingement plate were also varied parametrically. To facilitate the experiments, the naphthalene sublimation technique was employed, and the resulting mass transfer coefficients were converted to heat transfer coefficients by the well-established analogy between the two processes. It was found that the point of maximum mass transfer is displaced from the geometrical impingement point, with the extent of the displacement increasing with greater jet inclination. The local coefficients on the uphill side of the maximum point drop off more rapidly than do those on the downhill side, thus creating an imbalance in the cooling/heating capabilities on the two sides. Neither the maximum transfer coefficient nor the surface-averaged transfer coefficient are highly sensitive to the inclination of the jet; during the course of the experiments, the largest inclination-induced decreases in these quantities were in the 15 to 20 percent range.

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