Large Eddy Simulations on Fan Shaped Film Cooling Hole With Various Inlet Turbulence Generation Methods

2020 ◽  
Author(s):  
Young Seok Kang ◽  
Sangook Jun ◽  
Dong-Ho Rhee
Keyword(s):  
Vortex Structure ◽  
Film Cooling ◽  
Main Flow ◽  
Large Eddy Simulations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Large Eddy ◽  
Cooling Hole ◽  
Turbulence Generation

Abstract Large eddy simulations on well-known 7-7-7 fan shaped cooling hole have been carried out. Film cooling methods are generally applied to high pressure turbine, of which flow condition is extremely turbulent because high pressure turbines are generally located downstream combustor in gas turbines. However, different to RANS simulations, implementing turbulence at the main flow inlet is not simple in LES. For this reason, several numerical techniques have been devised to give turbulence information at the inlet boundary condition in LES. In this study, rectangular turbulator was located in front of the cooling hole to generate turbulent boundary flow in the main flow. Another method used in this study is transient table method to simulate turbulent flow at the main flow inlet. Without turbulent velocity components in approaching flow, laterally discharged cooling flow touches wall while it forms a vortex structure. Then high film cooling effectiveness region around the cooling hole appears. In the meanwhile, when approaching flow is turbulent, the laterally discharged cooling flow no more forms vortex structure and dissipated to the main flow and resultant high effectiveness region disappears. Both turbulence generation methods showed that turbulent intensity of the main flow affects effective range of the cooling flow and resultant film cooling effectiveness distributions. Also high turbulence intensity of the main flow stimulates early break down of the vortex structure coming out of the cooling hole and its dissipation to the main flow. It means high turbulent intensity restricts film cooling flow coverage. Another lesson from the study is that vortex generated from the cooling hole, its development and dissipation to the main flow, have an important role to understand film cooling effectiveness distributions around the cooling hole.

Large Eddy Simulations on Fan Shaped Film Cooling Hole with Upstream Boundary Layer Turbulence Effect Generated by Trip Strip

2021 ◽  
pp. 1-37
Author(s):  
Young Seok Kang ◽  
Sangook Jun ◽  
Dong-Ho Rhee
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Film Cooling ◽  
Main Flow ◽  
Large Eddy Simulations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Large Eddy ◽  
Cooling Hole

Abstract Large eddy simulations on the well-known 7-7-7 fan shaped cooling hole were carried out. Like using a trip strip to create turbulent boundary layer in practical experiments, trip strips with different configurations were placed upstream of the cooling hole to investigate incoming turbulent boundary layer effect on the film cooling flow behavior. Without the trip, horseshoe vortex generated by laminar boundary layer induced laterally discharging cooling flow in the lateral direction. Meanwhile, the induced cooling flow formed high film cooling effectiveness region around the film cooling hole. When the incoming boundary flow was turbulent, laterally discharged cooling flow was influenced by the turbulent boundary layer to dissipate to the main flow and resultant high effectiveness region disappeared. Depending on the trip configuration, quantitative characteristics of boundary layer such as turbulent intensity, momentum thickness and shape factor were strongly affected. Some trip configurations resulted in fully developed turbulent boundary layer just before leading edge of the film cooling hole. In such cases, distribution of the film cooling effectiveness showed a reasonable agreement with available experimental data where the quantitative properties of the turbulent boundary layer were similar. However, when the trip was located too close to the film cooling hole, the separated and reattached flow did not develop into the stabilized turbulent boundary layer. Then strong turbulence intensity in the main flow boundary layer stimulated break down of the cooling flow vortex structure and early dissipation to the main flow. It resulted in restricted film cooling flow coverage.

scholarly journals Large Eddy Simulations on Film Cooling Flow Behaviors with Upstream Turbulent Boundary Layer Generated by Circular Cylinder

Energies ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 7227
Author(s):  
Young Seok Kang ◽  
Dong-Ho Rhee ◽  
Yu Jin Song ◽  
Jae Su Kwak
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Film Cooling ◽  
Measured Data ◽  
Large Eddy Simulations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Large Eddy ◽  
Cooling Hole

Large eddy simulations on film cooling hole array on a flat plate was carried out to investigate upstream turbulence effect. Circular cylinders were configured to create a turbulent boundary layer and its diameter has been adjusted to generate 13% upstream turbulence intensity in the main flow. Due to the small pitch to diameter configuration of the cylinder, two-dimensional LES analysis was carried out in advance and the results showed that LES was an essential method to resolve flow field around and downstream circular cylinder, which was not available in RANS simulations. The three-dimensional LES results showed reasonable agreement in turbulence intensity and normalized velocity distributions along the vertical with measured data. According to the blowing ratio, the cooling flow coverage on the surface along the stream-wise direction was varied and well agreed with measured data. Additionally, upstream boundary flows were partially ingested inside the cooling hole and discharged again near along the centerline of the cooling hole. This accounted for film cooling effectiveness distribution inside the cooling hole surface and along the centerline. The current study revealed that the LES for predicting turbulent boundary layer behaviors due to upstream turbulence generation source was an effective and feasible method. Moreover, the LES effectively resolved flow fields such as film cooling flow behaviors and corresponding film cooling effectiveness distributions.

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

2011 ◽  
Author(s):  
Aaron F. Shinn ◽  
S. Pratap Vanka
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Wind Tunnel Experiments ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flows ◽  
Large Eddy

Large Eddy Simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported with the jet modeled using a plenum/pipe configuration. This configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

Numerical Study on Effects of Density Ratio on Film Cooling Flow Structure and Film Cooling Effectiveness

2017 ◽  
Author(s):  
Eiji Sakai ◽  
Toshihiko Takahashi
Keyword(s):  
Shear Layer ◽  
Film Cooling ◽  
Numerical Study ◽  
Density Ratio ◽  
Hairpin Vortices ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
High Density Ratio ◽  
Cooling Hole

To understand film cooling flow fields on a gas turbine blade, this paper reports a series of large-eddy simulations of an inclined round jet issuing into a crossflow. Simulations were performed at constant momentum ratio conditions, IR = 0.25, 0.5, 1.0 and Reynolds number, Re = 15,300, based on the crossflow velocity and the film cooling hole diameter. Density ratio, DR, is changed from 1.0 to 2.0, and effects of the density ratio on vortical structures around the film cooling hole exit and film cooling effectiveness are investigated. The results showed that the vortical structure of the ejected jet drastically changes with varying density ratio. When the density ratio is comparatively small, hairpin vortices are formed downstream of the hole exit. On the contrary, when the density ratio is comparatively high, the formation of the hairpin vortices is suppressed and jet shear layer vortices are formed on side edges of the cooling jet. The jet shear layer vortices conveys the coolant air to the wall surface. As a result, higher film cooling effectiveness is obtained at comparatively high density ratio conditions compared to comparatively low density ratio conditions. Additional simulations were performed to discuss a possibility of an improvement in the film cooling effectiveness by controlling the formation of the jet shear layer vortices.

Large Eddy Simulations for Film Cooling Assessment of Cylindrical and Laidback Fan-Shaped Holes With Reverse Injection

2020 ◽  
Vol 13 (3) ◽  
Author(s):  
Ashutosh Kumar Singh ◽  
Kuldeep Singh ◽  
Dushyant Singh ◽  
Niranjan Sahoo
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Large Eddy Simulations ◽  
Cylindrical Hole ◽  
Axial Velocity Component ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Injection Angle ◽  
Large Eddy ◽  
Shaped Hole

Abstract The large eddy simulations (LES) are performed to access the film cooling performance of cylindrical and reverse shaped hole for forward and reverse injection configurations. In the case of reverse/backward injection, the secondary flow is injected in such a way that its axial velocity component is in the direction opposite to mainstream flow. The study is carried out for a blowing ratio (M = 1), density ratio (DR = 2.42), and injection angle (α = 35 deg). Formation of counter-rotating vortex pair (CRVP) is one of the major issues in the film cooling. This study revealed that the CRVP found in the case of forward cylindrical hole which promotes coolant jet “liftoff” is completely mitigated in the case of the reverse shaped hole. The coolant coverage for reverse cylindrical and reverse shaped holes is uniform and higher. The reverse shaped hole shows promising results among investigated configurations. The lateral averaged film cooling effectiveness of reverse shaped hole is 1.16–1.42 times higher as compared to the forward shaped holes. The improvement in the lateral averaged film cooling effectiveness of reverse cylindrical hole (RCH) injection over forward cylindrical hole (FCH) injection is 1.33–2 times.

Large Eddy Simulation of Inclined Jet in Cross Flow With Cylindrical and Fan-Shaped Holes

2016 ◽  
Author(s):  
Lingxu Zhong ◽  
Chao Zhou ◽  
Shiyi Chen
Keyword(s):  
Temperature Distribution ◽  
Large Eddy Simulation ◽  
Film Cooling ◽  
Main Flow ◽  
Hairpin Vortices ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Coherent Vortices

A large eddy simulation (LES) investigation of the inclined jet in crossflow is presented in this paper. The angle between the hole and the main flow is 35 degrees, which represents a typical film cooling application. Two different geometries, namely the cylindrical hole and the fan-shaped hole, are investigated at a blowing ratio of 0.5, which is a representative value for film cooling. The numerical tool is first validated and then used to study the flow and the film cooling effectiveness of the cooling holes. Both the time averaged and the instantaneous flow characteristics are analyzed. In the time averaged results, the counter-rotating vortex pair has large effects on the mixing of the coolant with the main flow. The instantaneous results show that the mixing of the injected flow with the main flow is highly related to the unsteady coherent vortices. The difference in the cooling effectiveness distribution for the two holes is due to the different coherent vortices. The relationship between the coherent vortices and the temperature distribution is explained in detail. These results show that the vortices distribution at the exit of the hole has important influence on the later development of the hairpin vortices, thus affecting the temperature distribution and the cooling effectiveness.

Large Eddy Simulations of Film-Cooling Flows With a Micro-Ramp Vortex Generator

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Aaron F. Shinn ◽  
S. Pratap Vanka
Keyword(s):  
Film Cooling ◽  
Cross Flow ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Large Eddy Simulations ◽  
Wind Tunnel Experiments ◽  
Turbulent Structures ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Large Eddy

Large eddy simulations were performed to study the effect of a micro-ramp on an inclined turbulent jet interacting with a cross-flow in a film-cooling configuration. The micro-ramp vortex generator is placed downstream of the film-cooling jet. Changes in vortex structure and film-cooling effectiveness are evaluated. Coherent turbulent structures characteristic of a jet in a cross-flow are analyzed and the genesis of the counter-rotating vortex pair in the jet is discussed. Results are reported for two film-cooling configurations, where the primary difference is the way the jet inflow boundary conditions are prescribed. In the first configuration, the jet conditions are prescribed using a precursor simulation and in the second the jet is modeled using a plenum/pipe configuration. The latter configuration was designed based on previous wind tunnel experiments at NASA Glenn Research Center, and the present results are meant to supplement those experiments. It is found that the micro-ramp improves film-cooling effectiveness by generating near-wall counter-rotating vortices which help entrain coolant from the jet and transport it to the surface. The pair of vortices generated by the micro-ramp are of opposite sense to the vortex pair embedded in the jet.

scholarly journals Investigations on the effect of different influencing factors on film cooling effectiveness under the injection of synthetic coolant

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jianlong Chang ◽  
Xinlei Duan ◽  
Yang Du ◽  
Baoquan Guo ◽  
Yutian Pan
Keyword(s):  
Film Cooling ◽  
Elliptical Hole ◽  
Synthetic Jet ◽  
Cooling Effect ◽  
Flow Structures ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Flow ◽  
Cooling Method ◽  
Strong Controllability

AbstractBy combining the synthetic jet and film cooling, the incident cooling flow is specially treated to find a better film cooling method. Numerical simulations of the synthetic coolant ejected are carried out for analyzing the cooling performance in detail, under different blowing ratios, hole patterns, Strouhal numbers, and various orders of incidence for the two rows of holes. By comparing the flow structures and the cooling effect corresponding to the synthetic coolant and the steady coolant fields, it is found that within the scope of the investigations, the best cooling effect can be obtained under the incident conditions of an elliptical hole with the aspect ratio of 0.618, the blow molding ratio of 2.5, and the Strouhal number St = 0.22. Due to the strong controllability of the synthetic coolant, the synthetic coolant can be controlled through adjusting the frequency of blowing and suction, so as to change the interaction between vortex structures for improving film cooling effect in turn. As a result, the synthetic coolant ejection is more advisable in certain conditions to achieve better outcomes.

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