Influence of Mainstream Cross Flow on Film Cooling Performance and Jet Flow Field

2017 ◽  
Author(s):  
Yifei Li ◽  
Yang Zhang ◽  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Gas Turbines ◽  
Cross Flow ◽  
Jet Flow ◽  
Secondary Flows ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Significant Difference ◽  
The Cross

The influence of the cross flow in mainstream on film cooling performance and jet flow field is investigated experimentally and numerically. To show the effect of cross flow in mainstream without the influence of the other secondary flows, a curved test section is constructed to generate a cross flow, simulating the curved turbine passage. Both the straight and the curved passage are used to show the differences of cooling performance for shaped holes with and without the cross flow, with blowing ratio varying from M = 0.5 to M = 2.5. Pressure sensitive paint is used to measure the adiabatic cooling effectiveness, and the ink trace measurement is conducted to present the friction lines on the endwall platform. Numerical simulations are performed to show the flow field. The cross flow is accelerated in a curved passage and migrates the fluid near the endwall platform. Due to the cross flow in the mainstream, the deflection angle changes a lot along the normal direction to the endwall, and dominates the spatial distribution of coolant. Although the cooling trace follows the trend of wall surface streamlines, the migration of coolant is slower than the deviation of the friction line, and the difference increases with increasing blowing ratios. The cross flow enhances the lateral dispersion, decreasing the peak value of cooling effectiveness but increasing the laterally averaged cooling effectiveness. Higher blowing ratios lead to a higher intensity of a counter-rotating vortex pair that limits lateral dispersion near the outlet of cooling hole. But the effect of cross flow dominates the flow pattern downstream. The cooling performance has a significant difference with the influence of the cross flow. This study is essential to understand the interaction of the cross flow and the film cooling in gas turbines.

Experimental Investigation of Film Cooling Performance on Blade Endwall with Diffusion Slot Holes and Stator-Rotor Purge Flow

2021 ◽  
pp. 1-28
Author(s):  
Zhi-Qiang Yu ◽  
Jianjun Liu ◽  
Chen Li ◽  
Baitao An ◽  
Guang-Yao Xu
Keyword(s):  
Film Cooling ◽  
Flow Direction ◽  
Cross Flow ◽  
Orientation Angle ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Pressure Surface ◽  
Blowing Ratio ◽  
Shaped Hole

Abstract This paper focuses on the influences of the discrete hole shape and layout on the blade endwall film cooling effectiveness. The diffusion slot hole was first applied to the blade endwall and compared with the fan-shaped hole. The effect of upstream purge slot injection on the film cooling performance of the discrete hole was also investigated. Experiments were performed in a linear cascade with a exit Reynolds number of 2.64×105. The film cooling effectiveness on the blade endwall were measured by the pressure sensitive paint technique. Results indicate that the diffusion slot hole significantly increases the film cooling effectiveness on the blade endwall compared to the fan-shaped hole, especially at high blowing ratio. The maximum relative increment of the cooling effectiveness is over 40%. The layout with the discrete holes arranged lining up with the tangent direction of the blade profile offset curves exhibits a comparable film cooling effectiveness with the layout with the discrete holes arranged according to the cross-flow direction. The film cooling effectiveness on the pressure surface corner is remarkably enhanced by deflecting the hole orientation angle towards the pressure surface. The combination of purge slot and diffusion slot holes supplies a full coverage film cooling for the entire blade endwall at coolant mass flow ratio of the purge slot of 1.5% and blowing ratio of 2.5. In addition, the slot injection leads to a non-negligible influence on the cooling performance of the discrete holes near the separation line.

Experimental Investigation of Film Cooling Performance on Blade Endwall With Diffusion Slot Holes and Stator-Rotor Purge Flow

2020 ◽  
Author(s):  
Zhiqiang Yu ◽  
Jianjun Liu ◽  
Chen Li ◽  
Baitao An ◽  
Guangyao Xu
Keyword(s):  
Film Cooling ◽  
Flow Direction ◽  
Cross Flow ◽  
Orientation Angle ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Pressure Surface ◽  
Offset Curves ◽  
Shaped Hole

Abstract This paper focuses on the influences of the discrete hole shape and layout on the blade endwall film cooling effectiveness. The effect of upstream purge slot injection on the film cooling performance of the discrete hole was also investigated. The diffusion slot hole was first applied to the blade endwall. As a comparison, the cooling performance of the fan-shaped hole was also measured. Totally, six discrete-hole cooling configurations (2 hole shapes × 3 layouts) were investigated. Experiments were performed in a seven-blade linear cascade with the exit Reynolds number of 2.64 × 105. The average blowing ratios (BR) of the discrete holes changed from 0.5 to 2.5, and the coolant mass flow ratio of the purge slot (MFR) was fixed at MFR = 1.5%. The distributions of the cooling effectiveness on the blade endwall were measured by the pressure sensitive paint technique. Results indicate that the diffusion slot hole significantly increases the film cooling effectiveness on the blade endwall compared to the fan-shaped hole, especially at high blowing ratio. The maximum relative increment of the cooling effectiveness is over 40%. The layout with the discrete holes arranged lining up with the tangent direction of the blade profile offset curves exhibits a comparable film cooling effectiveness with the layout with the discrete holes arranged according to the cross-flow direction. The film cooling effectiveness on the pressure surface corner is remarkably enhanced by deflecting the hole orientation angle towards the pressure surface. The combination of purge slot and diffusion slot holes supplies a full coverage film cooling for the entire blade endwall at MFR = 1.5% and BR = 2.5. In addition, the slot injection leads to a non-negligible influence on the cooling performance of the discrete holes near the separation line.

Investigations on the Influence of Rib Orientation Angle on Film Cooling Performance of Cylindrical Holes

2017 ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Hui-ren Zhu ◽  
Jian-xia Luo ◽  
Ying-ni Zhai
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Discharge Coefficient ◽  
Cross Flow ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Flow Channels ◽  
Cylindrical Holes

This paper presents an experimental and numerical investigation on the film cooling with different coolant feeding channel structures. Two ribbed cross-flow channels with rib-orientation of 135° and 45° respectively and the plenum coolant channel have been studied and compared to find out the effect of rib orientation on the film cooling performances of cylindrical holes. The film cooling effectiveness and heat transfer coefficient were measured by the transient heat transfer measurement technique with narrow-band thermochromic liquid crystal. Numerical simulations with realizable k-ε turbulence model were also performed to analyze the flow mechanism. The results show that the coolant channel structure has a notable effect on the flow structure of film jet which is the most significant mechanism affecting the film cooling performance. Generally, film cooling cases fed with ribbed cross-flow channels have asymmetric counter-rotating vortex structures and related asymmetric temperature distributions, which make the film cooling effectiveness and the heat transfer coefficient distributions asymmetric to the hole centerline. The discharge coefficient of the 45° rib case is the lowest among the three cases under all the blowing ratios. And the plenum case has higher discharge coefficient than the 135° rib case under low blowing ratio. With the increase of blowing ratio, the discharge coefficient of the 135° rib case gets larger than the plenum case gradually, because the vortex in the upper half region of the coolant channel rotates in the same direction with the film hole inclination direction and makes the jet easy to flow into the film hole in the 135° rib case.

An Experimental Study of Mist/Air Film Cooling on a Flat Plate With Application to Gas Turbine Airfoils: Part 1 — Heat Transfer

2013 ◽  
Author(s):  
Lei Zhao ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Thermal Stresses ◽  
Test Facility ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Blowing Ratio ◽  
Turbine Airfoils ◽  
Air Film

Film cooling is a cooling technique widely used in high-performance gas turbines to protect the turbine airfoils from being damaged by hot flue gases. Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments in this study. A small amount of tiny water droplets (7% wt.) with an average diameter about 5 μm (mist) is injected into the cooling air to enhance the cooling performance. A wind tunnel system and test facility is specifically built for this unique experiment. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part 1 is focused on the heat transfer result on the wall and Part 2 is focused on the two-phase droplet multiphase flow behavior. Mist film cooling performance is evaluated and compared against air-only film cooling in terms of adiabatic film cooling effectiveness and film coverage. A row of five circular cylinder holes is used, injecting at an inclination angle of 30° into the main flow. For the 0.6 blowing ratio cases, it is found that adding mist performs as wonderfully as we mindfully sought: the net enhancement reaches a maximum 190% locally and 128% overall at the centerline, the cooling coverage increases by 83%, and more uniform surface temperature is achieved. The latter is critical for reducing wall thermal stresses. When the blowing ratio increases from 0.6 to 1.4, both the cooling coverage and net enhancement are reduced to below 60%. Therefore, it is more beneficial to choose a relatively low blowing ratio to keep the coolant film attached to the surface when applying the mist cooling. The concept of Film Decay Length (FDL) is introduced and proven to be a useful guideline to quantitatively evaluate the effective cooling coverage and cooling decay rate.

Directed Particle-Laden Micro-Jet for Dental Caries Evacuation (Keynote Paper)

2003 ◽  
Author(s):  
Michael Amitay ◽  
Shayne Kondor ◽  
Scott Herdic ◽  
Steven L. Anderson
Keyword(s):  
Dental Caries ◽  
Flow Field ◽  
Active Control ◽  
High Speed ◽  
Cross Flow ◽  
Jet Flow ◽  
Spreading Rate ◽  
Exit Plane ◽  
Keynote Paper ◽  
The Cross

Active and passive approaches to control the velocity and concentration of a high speed round particle-laden jet are investigated experimentally using a stereo PIV system. Active control of the flow field and the particles’ velocity and concentration fields, via the addition of swirl to the carrier jet, has shown to have a significant effect in altering both phases. Control is also affected by placing passive pins at the jet exit plane, which results in alteration of the velocity in planes across and normal to the pins. Furthermore, the mixing is increased and the spreading rate is modified. Depending on the number of pins used and their azimuthal location, their interaction with the carrier jet flow lead to the modification of the cross-flow shape of the jet and the direction of the flow.

Influence of Laser Drilling Imperfection on Film Cooling Performances

2005 ◽  
Author(s):  
Milenko B. Jovanovic´ ◽  
Hendrik C. de Lange ◽  
Anton A. van Steenhoven
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Particle Image ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Vortical Structures ◽  
Liquid Crystal Thermography ◽  
Image Velocimetry

Film cooling is studied on a jet in a cross-flow. The influence of a hole production imperfection on the jet-cross flow interaction is investigated experimentally by means of particle image velocimetry and liquid crystal thermography. To simulate the imperfection a half torus was placed inside the hole. The experiments were conducted with and without the production imperfection and the velocity ratio was varied. If the imperfection is absent, vortices are generated by means of the Kelvin-Helmholtz instability and separation on the hole trailing edge. The imperfection produces additional vortical structures and the flow field starts to oscillate. The deteriorated flow field changes the heat transfer. Surface temperature measurements show that the production imperfection reduces the film cooling effectiveness. The influence of the production imperfection on the film cooling effectiveness decreases with the enhanced velocity ratio.

Heat Transfer and Fluid Flow of a Single Jet Impingement in Cross-Flow Modified by a Vortex Generator Pair

2016 ◽  
Author(s):  
Chenglong Wang ◽  
Lei Luo ◽  
Lei Wang ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Gas Turbines ◽  
Cross Flow ◽  
Vortex Generator ◽  
Jet Impingement ◽  
Transfer Coefficients ◽  
Stagnation Region ◽  
Target Wall ◽  
The Cross

Jet impingement cooling is widely used in modern gas turbines. In the present study, both heat transfer and flow field measurements of jet impingement in cross-flow are carried out with and without a vortex generator pair (VGP). The jet and cross-flow Reynolds numbers are fixed at 15,000 and 48,000, respectively. The local heat transfer coefficients are obtained by a liquid crystal thermography (LCT) technique. Results show that the jet impingement heat transfer on the target wall is remarkably enhanced by the VGP as compared to the baseline case. The stagnation region moves upstream with improved heat transfer when the VGP is present. The flow field is measured by particle image velocimetry (PIV). The cross-flow is shown to deflect the impinging jet but the VGP reduces the streamwise momentum of the cross-flow and drives the crossflow away from the issuing jet. This leads to stronger jet impingement and thus heat transfer enhancement on the target wall.

CFD Simulations for Film Cooling Holes: Comparison Between Different Isotropic and Anisotropic Eddy Viscosity Models

2018 ◽  
Author(s):  
Jens Dickhoff ◽  
Karsten Kusterer ◽  
Santhosh Kumar Bhaskar ◽  
Dieter Bohn
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Constitutive Relations ◽  
Turbulence Models ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Acceptable Accuracy ◽  
Cooling Hole

In modern gas turbines, film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). Within the past decade, the technology has been improved step by step at B&B-AGEMA and Kawasaki Heavy Industries Ltd.; mainly by means of numerical simulations. The laterally averaged film cooling effectiveness is typically captured with acceptable accuracy, but the experimental measurements still show a deviation from the numerically obtained results with respect to the local film cooling effectiveness distribution behind the film cooling hole. Nevertheless, the film cooling air spread out in the lateral direction is one of the keys for enhancement of the film cooling performance. Thus, more precise simulations are consequently necessary for improvement of the hole shape configuration. The present study involves simulations of a baseline fan shaped hole configuration (“777 hole” investigated by Schroeder and Thole [1][2]) using different turbulence models available in STAR-CCM+ with isotropic and anisotropic turbulence consideration (constitutive relations). Distinct differences with respect to flow phenomena (detachments and vortex creation) can be observed depending on the applied turbulence model. In total, the results show that anisotropic viscosity strongly influences the film cooling performance prediction by CFD for prediction of the film cooling effectiveness, but none of the models provides acceptable accuracy in this regard.

Automated Design Space Exploration of Advanced-Shaped Film Cooling Holes Using the SHERPA Algorithm

2016 ◽  
Author(s):  
Karsten Kusterer ◽  
Jens Dickhoff ◽  
Noël T. Campana ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Design Space Exploration ◽  
Design Space ◽  
Cross Flow ◽  
Design Parameters ◽  
Test Case ◽  
Lateral Direction ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

In modern gas turbines, the film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). As a result, the cooling air remains close to the wall and spreads in lateral direction along the surface. The ACRV result from the specialized shape of the expanding hole exits (NEKOMIMI-shape). Thus, the design parameters have a crucial impact to the film cooling effectiveness behind the hole. In the present study the design parameters are varied and in order to explore the design space for a defined test case with respect to the maximum achievable averaged adiabatic film cooling effectiveness. This illustrates the capabilities of the technology. Additionally, the design space of a laidback fan-shaped film cooling configuration is explored and compared to the result obtained with the NEKOMIMI-shaped geometry. In order to show the robustness of the configurations with respect to compound angles of the cross flow, two advanced configurations — one NEKOMIMI and one shaped hole — are analysed with compound angles up to 16°.

scholarly journals Numerical Analysis of Film Cooling Performance of Micro Holes and Compound Angle Sister Holes

2021 ◽  
Author(s):  
Sana Milud Muftah Abd Alsalam
Keyword(s):  
Flow Field ◽  
Film Cooling ◽  
Turbulence Models ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Micro Holes ◽  
Micro Hole ◽  
Compound Angle

In the present research, micro holes and compound angle sister holes have been numerically investigated as two different techniques to enhance the cylindrical hole cooling performance, which suffers from a low cooling performance at high blowing ratio. The numerical analysis is performed over a flat plate model to assess the film effectiveness and the associated flow field at low and high blowing ratios. The performance assessment of the discrete round micro hole with a 200 µm diameter reveals that the micro hole yields the best cooling performance at low blowing ratios, and there is nearly 30% increase in the overall film cooling effectiveness compared to that of the round macro hole. The flow field results demonstrate the presence of a Counter-Rotating Vortex Pair (CRVP) at a smaller size and less strength, thus, contributed to better spanwise spreading of the coolant jet and lateral film cooling effectiveness. Micro holes present an improvement in the lateral film cooling effectiveness at high freestream turbulence intensity and high blowing ratios. Computational evaluation of the CFD prediction capability of the sister holes cooling effectiveness using five RANS turbulence models has been carried out as well as an assessment of the effects of the near-wall modeling on the predicted lateral effectiveness. The turbulence models used are realizable k-epsilon, standard k-epsilon, RNG k-epsilon, Reynolds stress model, and Spalart-Allmaras model. It is generally found that realizable k-ε combined with the enhanced wall treatment provides the best prediction of the numerical results in comparison to the experimental measurements at a low blowing ratio while an underprediction of the lateral performance is found at a high blowing ratio from all examined turbulence models. The compound angle upstream sister holes (CAUSH) have been proposed as a novel and simple design of the cooling hole whereas the numerical results have shown a notable increase in both centerline and lateral effectiveness for all tested compound angles at all blowing ratios. The anti-counter rotating vortices pair (ACRVP) structure generated from the compound angle upstream sister holes has actively controlled the flow field and maintained the coolant jet fully attached to the plate surface while restraining the coolant lift-off at high blowing ratios. Finally, the influence of the compound angle sister holes streamwise location on the thermal and flow field performance has also been analyzed, whereas three locations: upstream, midstream, and downstream are examined. It is found that the midstream and downstream locations offered a considerable increase in the cooling effectiveness, which is very much dependent on the blowing ratio and the area downstream of the cooling holes. In addition, the optimum centerline effectiveness is obtained by the downstream location, while the best lateral effectiveness is attained through the midstream location.

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