Simulations of Film Cooling Flow Structure and Heat Transfer in the Near Field of Cooling Jets With a Modified DES Model

Single Hole ◽

Film Cooling Holes ◽

Des Model

Abstract Simulations of film cooling in the near field (x/D < 15) of coolant jets on a flat plate are carried out with detached eddy simulation (DES) and modified DES models. The time-averaged unsteady film cooling effectiveness is compared with experimental data. Both models use two-layer zonal model for near-wall treatment. The near field critical turbulent flow behaviors such as mainstream entrainment, spanwise spreading of counter rotating vortex pair (CRVP), and vortical structure evolutions are predicted and analyzed by DES and modified DES in this study. Modified DES model differs from the DES by implementing an increased eddy viscosity in the spanwise direction to enhance spanwise-diffusion of film cooling jets. Detailed comparisons of DES and modified DES modeling results are made under density ratios of 2.0, 1.6, 1.2 and blowing ratio of 1.0 for a single hole. Modified DES model predicts a wider spanwise spreading of temperature field and film cooling effectiveness. In a comparison of spanwise-averaged film cooling effectiveness with experimental data, DES and modified DES models predict 14.8% and 10.4% deviations under density ratio of 2.0. For density ratio of 1.2, the DES and modified DES results deviate from data 24.5% and 14.7% respectively. Then simulation of film cooling with a three hole domain is also carried out. Instantaneous effectiveness results show that the jets from nearby film cooling holes start to interact with each other before x/D < 10. When the interactions of flow from film cooling holes next to each other are strong, simulations using several cooling holes are meaningful and the current study shows the difference of multi hole and single hole simulations.

Improved Film Cooling Effectiveness With a Round Film Cooling Hole Embedded in a Contoured Crater

Journal of Turbomachinery ◽

10.1115/1.4030395 ◽

2015 ◽

Vol 137 (10) ◽

Cited By ~ 12

Author(s):

Prasad Kalghatgi ◽

Sumanta Acharya

Keyword(s):

Film Cooling ◽

Near Field ◽

Density Ratio ◽

Cooling Effectiveness ◽

Field Development ◽

Eddy Simulation ◽

Baseline Case ◽

Cooling Hole ◽

Studies of film cooling holes embedded in craters and trenches have shown significant improvements in the film cooling performance. In this paper, a new design of a round film cooling hole embedded in a contoured crater is proposed for improved film cooling effectiveness over existing crater designs. The proposed design of the contour aims to generate a pair of vortices that counter and diminish the near-field development of the main kidney-pair vortex generated by the film cooling jet. With a weakened kidney-pair vortex, the coolant jet is expected to stay closer to the wall, reduce mixing, and therefore increase cooling effectiveness. In the present study, the performance of the proposed contoured crater design is evaluated for depth between 0.2D and 0.75D. A round film cooling hole with a 35 deg inclined short delivery tube (l/D = 1.75), freestream Reynolds number ReD = 16,000, and density ratio of coolant to freestream fluid ρj/ρ∞ = 2.0 is used as the baseline case. Hydrodynamic and thermal fields for all cases are investigated numerically using large eddy simulation (LES) technique. The baseline case results are validated with published experimental data. The performance of the new crater design for various crater depths and blowing ratios are compared with the baseline case. Results are also compared with other reported crater designs with similar flow conditions and crater depth. Performance improvement in cooling effectiveness of over 100% of the corresponding baseline case is observed for the contoured crater.

Simulation of Film Cooling Heat Transfer and Simulation Improvement With a Modified DES Turbulence Model

Volume 8A: Heat Transfer and Thermal Engineering ◽

10.1115/imece2018-86887 ◽

2018 ◽

Author(s):

Feiyan Yu ◽

Savas Yavuzkurt

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Film Cooling ◽

Cooling System ◽

Near Field ◽

Density Ratio ◽

Computational Cost ◽

Computational Time ◽

Spanwise Direction ◽

Des Model

Modeling the heat transfer characteristics of the highly turbulent flow in gas turbine film cooling is important for better engineering solutions to the film cooling system design. URANS, LES, DES and modified DES models capability in simulating film cooling with a density ratio of 2.0 and blowing ratio of 1.0 are studied in this work. Detailed comparisons of simulation results with experimental data regarding the near-field and far-fields are made. For near field predictions, DES gives decent prediction with a 21.4 % deviation of centerline effectiveness, while LES and URANS have deviation of 33.6% and 51.2% compared to the experimental data. Despite good predictions for near field, DES under predicts the spanwise spreading of counter rotating vortex pair and temperature field, therefore it over predicts the centerline effectiveness in the far field. To compensate for this shortcoming of DES, the eddy viscosity in the spanwise direction is increased to enhance spanwise-diffusion of the cooling jets. The modified DES prediction of overall centerline effectiveness deviates 12.4% from experimental data, while LES, unmodified DES and URANS predictions deviate 10.8%, 31.9% and 46.9%. The modified DES model has adequate predictions of vortices evolutions which URANS modeling lacks and consumes significant less computational time than LES. It can be said that the modified DES model results in satisfactory film cooling modeling with a moderate computational cost and time.

Influence of Coolant Density on Turbine Blade Film Cooling at Transonic Cascade Flow Conditions Using the Pressure Sensitive Paint Technique

10.1115/gt2021-59366 ◽

2021 ◽

Author(s):

Izhar Ullah ◽

Sulaiman M. Alsaleem ◽

Lesley M. Wright ◽

Chao-Cheng Shiau ◽

Je-Chin Han

Keyword(s):

Film Cooling ◽

Density Ratio ◽

Pressure Side ◽

Pressure Sensitive Paint ◽

Cooling Effectiveness ◽

Blowing Ratio ◽

Pressure Sensitive ◽

Blade Tip ◽

Abstract This work is an experimental study of film cooling effectiveness on a blade tip in a stationary, linear cascade. The cascade is mounted in a blowdown facility with controlled inlet and exit Mach numbers of 0.29 and 0.75, respectively. The free stream turbulence intensity is measured to be 13.5 % upstream of the blade’s leading edge. A flat tip design is studied, having a tip gap of 1.6%. The blade tip is designed to have 15 shaped film cooling holes along the near-tip pressure side (PS) surface. Fifteen vertical film cooling holes are placed on the tip near the pressure side. The cooling holes are divided into a 2-zone plenum to locally maintain the desired blowing ratios based on the external pressure field. Two coolant injection scenarios are considered by injecting coolant through the tip holes only and both tip and PS surface holes together. The blowing ratio (M) and density ratio (DR) effects are studied by testing at blowing ratios of 0.5, 1.0, and 1.5 and three density ratios of 1.0, 1.5, and 2.0. Three different foreign gases are used to create density ratio effect. Over-tip flow leakage is also studied by measuring the static pressure distributions on the blade tip using the pressure sensitive paint (PSP) measurement technique. In addition, detailed film cooling effectiveness is acquired to quantify the parametric effect of blowing ratio and density ratio on a plane tip design. Increasing the blowing ratio and density ratio resulted in increased film cooling effectiveness at all injection scenarios. Injecting coolant on the PS and the tip surface also resulted in reduced leakage over the tip. The conclusions from this study will provide the gas turbine designer with additional insight on controlling different parameters and strategically placing the holes during the design process.

Effect of Density Ratio on Film-Cooling Effectiveness Distribution and Its Uniformity for Several Hole Geometries on a Flat Plate

Journal of Turbomachinery ◽

10.1115/1.4041810 ◽

2019 ◽

Vol 141 (5) ◽

Cited By ~ 3

Author(s):

Jiaxu Yao ◽

Jin Xu ◽

Ke Zhang ◽

Jiang Lei ◽

Lesley M. Wright

Keyword(s):

Flat Plate ◽

Film Cooling ◽

Density Ratio ◽

Lateral Spread ◽

Spanwise Direction ◽

Cooling Effectiveness ◽

Cylindrical Holes ◽

Density Ratios ◽

Compound Angle

The film cooling effectiveness distribution and its uniformity downstream of a row of film cooling holes on a flat plate are investigated by pressure sensitive paint (PSP) under different density ratios. Several hole geometries are studied, including streamwise cylindrical holes, compound-angled cylindrical holes, streamwise fan-shape holes, compound-angled fan-shape holes, and double-jet film-cooling (DJFC) holes. All of them have an inclination angle (θ) of 35 deg. The compound angle (β) is 45 deg. The fan-shape holes have a 10 deg expansion in the spanwise direction. For a fair comparison, the pitch is kept as 4d for the cylindrical and the fan-shape holes, and 8d for the DJFC holes. The uniformity of effectiveness distribution is described by a new parameter (Lateral-Uniformity, LU) defined in this paper. The effects of density ratios (DR = 1.0, 1.5 and 2.5) on the film-cooling effectiveness and its uniformity are focused. Differences among geometries and effects of blowing ratios (M = 0.5, 1.0, 1.5, and 2.0) are also considered. The results show that at higher density ratios, the lateral spread of the discrete-hole geometries (i.e., the cylindrical and the fan-shape holes) is enhanced, while the DJFC holes is more advantageous in film-cooling effectiveness. Mostly, a higher lateral-uniformity is obtained at DR = 2.5 due to better coolant coverage and enhanced lateral spread, but the effects of the density ratio on the lateral-uniformity are not monotonic in some cases. Utilizing the compound angle configuration leads to an increased lateral-uniformity due to a stronger spanwise motion of the jet. Generally, with a higher blowing ratio, the lateral-uniformity of the discrete-hole geometries decreases due to narrower traces, while that of the DJFC holes increases due to a stronger spanwise movement.

Enhancement of Film Cooling Performance at the Leading Edge of Turbine Blade

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2006-90321 ◽

2006 ◽

Cited By ~ 6

Author(s):

K.-S. Kim ◽

Youn J. Kim ◽

S.-M. Kim

Keyword(s):

Turbine Blade ◽

Film Cooling ◽

Density Ratio ◽

Leading Edge ◽

Cylindrical Body ◽

Spanwise Direction ◽

Cooling Effectiveness ◽

Cooling Performance ◽

Blowing Ratio

To enhance the film cooling performance in the vicinity of the turbine blade leading edge, the flow characteristics of the film-cooled turbine blade have been investigated using a cylindrical body model. The inclination of the cooling holes is along the radius of the cylindrical wall and 20 deg relative to the spanwise direction. Mainstream Reynolds number based on the cylinder diameter was 1.01×105 and 0.69×105, and the mainstream turbulence intensities were about 0.2% in both Reynolds numbers. CO2 was used as coolant to simulate the effect of density ratio of coolant-to-mainstream. Furthermore, the effect of coolant flow rates was studied for various blowing ratios of 0.4, 0.7, 1.1, and 1.4, respectively. In experiment, spatially-resolved temperature distributions along the cylindrical body surface were visualized using infrared thermography (IRT) in conjunction with thermocouples, digital image processing, and in situ calibration procedures. This comparison shows the results generated to be reasonable and physically meaningful. The film cooling effectiveness of current measurement (0.29 mm × 0.33 min per pixel) presents high spatial and temperature resolutions compared to other studies. Results show that the blowing ratio has a strong effect on film cooling effectiveness and the coolant trajectory is sensitive to the blowing ratio. The local spanwise-averaged effectiveness can be improved by locating the first-row holes near the second-row holes.

Film Cooling Measurements for a Laidback Fan-Shaped Hole: Effect of Coolant Crossflow on Cooling Effectiveness and Heat Transfer

Journal of Turbomachinery ◽

10.1115/1.4041655 ◽

2019 ◽

Vol 141 (4) ◽

Cited By ~ 1

Author(s):

Marc Fraas ◽

Tobias Glasenapp ◽

Achmed Schulz ◽

Hans-Jörg Bauer

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Film Cooling ◽

Gas Flow ◽

Density Ratio ◽

Coolant Flow ◽

Cooling Effectiveness ◽

Cooling Hole ◽

Internal coolant passages of gas turbine vanes and blades have various orientations relative to the external hot gas flow. As a consequence, the inflow of film cooling holes varies as well. To further identify the influencing parameters of film cooling under varying inflow conditions, the present paper provides detailed experimental data. The generic study is performed in a novel test rig, which enables compliance with all relevant similarity parameters including density ratio. Film cooling effectiveness as well as heat transfer of a 10–10–10 deg laidback fan-shaped cooling hole is discussed. Data are processed and presented over 50 hole diameters downstream of the cooling hole exit. First, the parallel coolant flow setup is discussed. Subsequently, it is compared to a perpendicular coolant flow setup at a moderate coolant channel Reynolds number. For the perpendicular coolant flow, asymmetric flow separation in the diffuser occurs and leads to a reduction of film cooling effectiveness. For a higher coolant channel Reynolds number and perpendicular coolant flow, asymmetry increases and cooling effectiveness is further decreased. An increase in blowing ratio does not lead to a significant increase in cooling effectiveness. For all cases investigated, heat transfer augmentation due to film cooling is observed. Heat transfer is highest in the near-hole region and decreases further downstream. Results prove that coolant flow orientation has a severe impact on both parameters.

Unsteady Wake and Coolant Density Effects on Turbine Blade Film Cooling Using PSP Technique

2010 14th International Heat Transfer Conference, Volume 5 ◽

10.1115/ihtc14-22911 ◽

2010 ◽

Cited By ~ 3

Author(s):

Akhilesh P. Rallabandi ◽

Shiou-Jiuan Li ◽

Je-Chin Han

Keyword(s):

Film Cooling ◽

Density Ratio ◽

Leading Edge ◽

Suction Side ◽

Suction Surface ◽

Cooling Effectiveness ◽

Unsteady Wake ◽

Lift Off ◽

The effect of an unsteady stator wake (simulated by wake rods mounted on a spoke wheel wake generator) on the modeled rotor blade is studied using the Pressure Sensitive Paint (PSP) mass transfer analogy method. Emphasis of the current study is on the mid-span region of the blade. The flow is in the low Mach number (incompressible) regime. The suction (convex) side has simple angled cylindrical film-cooling holes; the pressure (concave) side has compound angled cylindrical film cooling holes. The blade also has radial shower-head leading edge film cooling holes. Strouhal numbers studied range from 0 to 0.36; the exit Reynolds Number based on the axial chord is 530,000. Blowing ratios range from 0.5 to 2.0 on the suction side; 0.5 to 4.0 on the pressure side. Density ratios studied range from 1.0 to 2.5, to simulate actual engine conditions. The convex suction surface experiences film-cooling jet lift-off at higher blowing ratios, resulting in low effectiveness values. The film coolant is found to reattach downstream on the concave pressure surface, increasing effectiveness at higher blowing ratios. Results show deterioration in film cooling effectiveness due to increased local turbulence caused by the unsteady wake, especially on the suction side. Results also show a monotonic increase in film-cooling effectiveness on increasing the coolant to mainstream density ratio.

Enhanced Film Cooling Effectiveness With Surface Trenches

Volume 3B: Heat Transfer ◽

10.1115/gt2013-94530 ◽

2013 ◽

Cited By ~ 1

Author(s):

K. Vighneswara Rao ◽

Jong S. Liu ◽

Daniel C. Crites ◽

Luis A. Tapia ◽

Malak F. Malak ◽

...

Keyword(s):

Film Cooling ◽

Density Ratio ◽

Operating Conditions ◽

Airfoil Surface ◽

Cooling Effectiveness ◽

Ansys Cfx ◽

Cooling Hole ◽

Computational Fluid Dynamics Cfd ◽

In this study, cylindrical and fan shaped film cooling holes are evaluated on the blade surface numerically, using the Computational Fluid Dynamics (CFD) tool ANSYS-CFX, with the objective of improving cooling effectiveness by understanding the flow pattern at the cooling hole exit. The coolant flow rates are adjusted for blowing ratios of 0.5, 1.0 & 1.5 (momentum flux ratios of 0.125, 0.5 & 1.125 respectively). The density ratio is maintained at 2.0. New shaped holes viz. straight, concave and convex trench holes are introduced and are evaluated under similar operating conditions. Results are presented in terms of surface temperatures and adiabatic effectiveness at three different blowing ratios for the different film cooling hole shapes analyzed. Comparison is made with reference to the fan shaped film cooling hole to bring out relative merits of different shapes. The new trench holes improved the film cooling effectiveness by allowing more residence time for coolant to spread laterally while directing smoothly onto the airfoil surface. While convex trench improved the centre-line effectiveness, straight trench improved the laterally-averaged and overall effectiveness at all blowing ratios. Concave trench improved the effectiveness at blowing ratios 0.5 and 1.0.

Unsteady Wake and Coolant Density Effects on Turbine Blade Film Cooling Using Pressure Sensitive Paint Technique

Journal of Heat Transfer ◽

10.1115/1.4006748 ◽

2012 ◽

Vol 134 (8) ◽

Cited By ~ 10

Author(s):

Akhilesh P. Rallabandi ◽

Shiou-Jiuan Li ◽

Je-Chin Han

Keyword(s):

Film Cooling ◽

Density Ratio ◽

Suction Side ◽

Pressure Sensitive Paint ◽

Suction Surface ◽

Cooling Effectiveness ◽

Pressure Sensitive ◽

Unsteady Wake ◽

The effect of an unsteady stator wake (simulated by wake rods mounted on a spoke-wheel wake generator) on the modeled rotor blade is studied using the pressure sensitive paint (PSP) mass-transfer analogy method. Emphasis of the current study is on the midspan region of the blade. The flow is in the low Mach number (incompressible) regime. The suction (convex) side has simple angled cylindrical film-cooling holes; the pressure (concave) side has compound angled cylindrical film-cooling holes. The blade also has radial shower-head leading edge film-cooling holes. Strouhal numbers studied range from 0 to 0.36; the exit Reynolds number based on the axial chord is 530,000. Blowing ratios range from 0.5 to 2.0 on the suction side and 0.5 to 4.0 on the pressure side. Density ratios studied range from 1.0 to 2.5, to simulate actual engine conditions. The convex suction surface experiences film-cooling jet lift-off at higher blowing ratios, resulting in low effectiveness values. The film coolant is found to reattach downstream on the concave pressure surface, increasing effectiveness at higher blowing ratios. Results show deterioration in film-cooling effectiveness due to increased local turbulence caused by the unsteady wake, especially on the suction side. Results also show a monotonic increase in film-cooling effectiveness on increasing the coolant to mainstream density ratio.

Influence of Hole Inlet Geometry on the Film Cooling Effectiveness From Shaped Film Cooling Holes

Volume 5B: Heat Transfer ◽

10.1115/gt2019-92057 ◽

2019 ◽

Author(s):

Travis B. Watson ◽

Kyle R. Vinton ◽

Lesley M. Wright ◽

Daniel C. Crites ◽

Mark C. Morris ◽

...

Keyword(s):

Film Cooling ◽

Density Ratio ◽

Lateral Spread ◽

Pressure Sensitive Paint ◽

Cooling Effectiveness ◽

Pressure Sensitive ◽

Inlet Geometry ◽

Cooling Hole ◽

Abstract The effect of film cooling hole inlet geometry is experimentally investigated in this study. Detailed film cooling effectiveness distributions are obtained on a flat plate using Pressure Sensitive Paint (PSP). The inlet of a traditional 12°-12°-12°, laidback, fanshaped hole varies from a traditional “round” opening to an oblong, racetrack shaped opening. In this study, a single racetrack inlet with an aspect ratio of 2:1 is compared to the round inlet. For both designs, the holes are inclined at θ = 30° relative to the mainstream. Blowing ratios of 0.5, 1.0, and 1.5 are considered as the coolant–to–mainstream density ratio varies between 1.0 and 4.0. For all cases, the freestream turbulence intensity is maintained at 7.5%. With the introduction of the racetrack shaped inlet, the coolant spreads laterally across the diffuse, laidback fanshaped outlet. The centerline film cooling effectiveness is reduced with the enhanced lateral spread of the coolant. However, the benefit of the shaped inlet is also observed with an increase in the area averaged film cooling effectiveness, compared to the traditional round inlet. Not only does the shaped inlet promote spreading of the coolant, it is also believed the racetrack shape suppresses turbulence within the hole allowing for enhanced film cooling protection near the film cooling holes.