scholarly journals Measurements of Mass Transfer Coefficient and Effectiveness in the Recovery Region of a Film-Cooled Surface

1986 ◽  
Author(s):  
W. P. Webster ◽  
S. Yavuzkurt
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Turbulent Boundary Layer ◽  
Film Cooling ◽  
Transfer Coefficients ◽  
Large Area ◽  
Mass Transfer Equation ◽  
Mass Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Naphthalene Sublimation Technique

Mass transfer coefficients and the film cooling effectiveness are measured downstream of a single row of holes inclined 30 degrees with the surface and inline with the main turbulent boundary layer flow. The mass transfer coefficients (based on the difference between the free stream and the surface concentrations) are measured using a naphthalene sublimation technique. The effectiveness is determined through the injection of a trace gas into the secondary (cooling jets) flow and measuring its concentration at the impermeable wall. Experiments are carried out in a subsonic, zero pressure gradient turbulent boundary layer, under isothermal conditions with three blowing ratios (Uj/U∞): 0.4, 0.8, and 1.2. The data is collected in a region 7 to 80 jet diameters downstream of the injection location. From the data on mass transfer coefficients and effectiveness obtained under the same flow conditions a general mass transfer equation is derived. This paper presents extensive data and discussions; and is believed to be one of the few studies in which both of these variables are measured on the same surface and in a large area in the recovery region.

Film Cooling Downstream of a Row of Discrete Holes With Compound Angle

2000 ◽  
Vol 123 (2) ◽  
pp. 222-230 ◽  
Author(s):  
R. J. Goldstein ◽  
P. Jin
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Film Cooling ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Mass Transfer Coefficients ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Compound Angle

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35 deg inclination angle and 45 deg compound angle with 3d hole spacing and relatively small hole length to diameter ratio (6.3). Both film cooling effectiveness and mass/heat transfer coefficients are determined for blowing rates from 0.5 to 2.0 with density ratio of unity. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with that of pure air injection. This technique enables one to obtain detailed local information on film cooling performance. General agreement is found in local film cooling effectiveness when compared with previous experiments. The laterally averaged effectiveness with compound angle injection is higher than that with inclined holes immediately downstream of injection at a blowing rate of 0.5 and is higher at all locations downstream of injection at larger blowing rates. A large variation of mass transfer coefficients in the lateral direction is observed in the present study. At low blowing rates of 0.5 and 1.0, the laterally averaged mass transfer coefficient is close to that of injection without compound angle. At the highest blowing rate used (2.0), the asymmetric vortex motion under the jets increases the mass transfer coefficient drastically ten diameters downstream of injection.

Film Cooling Downstream of a Row of Discrete Holes With Compound Angle

2000 ◽  
Author(s):  
R. J. Goldstein ◽  
P. Jin
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Film Cooling ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Mass Transfer Coefficients ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Compound Angle

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35° inclination angle and 45° compound angle with 3 diameter hole spacing and relatively small hole length to diameter ratio (6.3). Both film cooling effectiveness and mass/heat transfer coefficients are determined for blowing rates from 0.5 to 2.0 with density ratio of unity. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with that of pure air injection. This technique enables one to obtain detailed local information on film cooling performance. General agreement is found in local film cooling effectiveness when compared with previous experiments. The laterally-averaged effectiveness with compound angle injection is higher than that with inclined holes immediately downstream of injection at a blowing rate of 0.5 and is higher at all locations downstream of injection at larger blowing rates. A large variation of mass transfer coefficients in the lateral direction is observed in the present study. At low blowing rates of 0.5 and 1.0, the laterally-averaged mass transfer coefficient is close to that of injection without compound angle. At the highest blowing rate used (2.0), the asymmetrical vortex motion under the jets increases the mass transfer coefficient drastically ten diameters downstream of injection.

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.

Interactions of Film Cooling Rows: Effects of Hole Geometry and Row Spacing on the Cooling Performance Downstream of the Second Row of Holes

2003 ◽  
Author(s):  
Christian Saumweber ◽  
Achmed Schulz
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Large Scale ◽  
Density Ratio ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Staggered Arrangement ◽  
Film Cooling Holes

A comprehensive set of generic experiments is conducted to investigate the interaction of film cooling rows. Five different film cooling configurations are considered on a large scale basis each consisting of two rows of film cooling holes in staggered arrangement. The hole pitch to diameter ratio within each row is kept constant at P/D = 4. The spacing between the rows is either x/D = 10, 20, or 30. Fanshaped holes or simple cylindrical holes with an inclination angle of 30 deg. and a hole length of 6 hole diameters are used. With a hot gas Mach number of Mam = 0.3, an engine like density ratio of ρc/ρm = 1.75, and a freestream turbulence intensity of Tu = 5.1% are established. Operating conditions are varied in terms of blowing ratio for the upstream and, independently, the downstream row in the range 0.5<M<2.0. The results illustrate the importance of considering ejection into an already film cooled boundary layer. Adiabatic film cooling effectiveness and heat transfer coefficients are significantly increased. The decay of effectiveness with streamwise distance is much less pronounced downstream of the second row primarily due to pre-cooling of the boundary layer by the first row of holes. Additionally, a comparison of measured effectiveness data with predictions according to the widely used superposition model of Sellers [11] is given for two rows of fanshaped holes.

scholarly journals Aspects of Vane Film Cooling With High Turbulence: Part I — Heat Transfer

1997 ◽  
Author(s):  
Forrest E. Ames
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Film Cooling ◽  
Large Scale ◽  
Velocity Ratio ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Stagnation Region ◽  
Film Cooling Effectiveness ◽  
High Turbulence

A four vane subsonic cascade was used to investigate the influence of film injection on vane heat transfer distributions in the presence of high turbulence. The influence of high turbulence on vane film cooling effectiveness and boundary layer development was also examined in part II of this paper. A high level, large scale inlet turbulence was generated for this study with a mock combustor (12 %) and was used to contrast results with a low level (1 %) of inlet turbulence. The three geometries chosen to study in this investigation were one row and two staggered rows of downstream cooling on both the suction and pressure surfaces in addition to a showerhead array. Film cooling was found to have only a moderate influence on the heat transfer coefficients downstream from arrays on the suction surface where the boundary layer was turbulent. However, film cooling was found to have a substantial influence on heat transfer downstream from arrays in laminar regions of the vane such as the pressure surface, the stagnation region, and the near suction surface. Generally, heat transfer augmentation was found to scale on velocity ratio. In relative terms, the augmentation in the laminar regions for the low turbulence case was found to be higher than the augmentation for the high turbulence case. The absolute levels of heat transfer were always found to be the highest for the high turbulence case.

Heat (Mass) Transfer and Film Cooling Effectiveness With Injection Through Discrete Holes: Part II—On the Exposed Surface

1995 ◽  
Vol 117 (3) ◽  
pp. 451-460 ◽  
Author(s):  
H. H. Cho ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Film Cooling ◽  
Heat Mass Transfer ◽  
Saturated Vapor ◽  
Back Surface ◽  
Exposed Surface ◽  
Transfer Coefficients ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

The heat (mass) transfer coefficient and the film cooling effectiveness are obtained from separate tests using pure air and naphthalene-saturated vapor injected through circular holes into a crossflow of air. The experiments indicate that Sherwood numbers around the injection hole are up to four times those on a flat plate (without injection holes) due to the interaction of the jets and the mainstream. The mass transfer around the injection holes is dominated by formations of horseshoe, side, and kidney vortices, which are generated by the jet and crossflow interaction. For an in-line array of holes, the effectiveness is high and uniform in the streamwise direction but has a large variation in the lateral direction. The key parameters, including transfer coefficients on the back surface (Part I), inside the hole (Part I), and on the exposed surfaces, and the effectiveness on the exposed surface, are obtained so that the wall temperature distribution near the injection holes can be determined for a given heat flux condition. This detailed information will also aid the numerical modeling of flow and mass/heat transfer around film cooling holes.

Sign in / Sign up

Export Citation Format

Share Document