Effects of Oscillations in the Main Flow due to Thermo Acoustic Fields in a Gas Turbine Combustor on Film Cooling

2016 ◽  
Author(s):  
Seung Il Baek ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Gas Turbine ◽  
Flow Rate ◽  
Film Cooling ◽  
Jet Flow ◽  
Main Flow ◽  
Wave Form ◽  
Gas Turbine Combustor ◽  
Wave Forms

The objective of this study is to understand the effects of oscillations in the main flow and the film cooling jets caused by the thermoacoustic fields formed in a gas turbine combustor on film cooling. As a first step, CFD simulations are performed for the case of steady mainstream and steady film cooling jets for validation of models and simulations and compared with other studies trying to predict adiabatic effectiveness under similar operating conditions. Based on the knowledge gained on the capability and limitations of different turbulence models for the steady simulations, simulations were extended to unsteady main flow and unsteady cooling jets. The unsteady simulations are performed using URANS-realizable k-ε turbulence model and LES-Smagorinsky-Lilly model. Initially, oscillations due to the combustion instabilities are approximated to be in sinusoidal form. For unsteady main flow and cooling jet simulations, results from the Seo et al. [3] experimental study were selected for comparison with CFD results. The effects of different frequencies (2, 16, 32 Hz) on film cooling are investigated. In each case, average blowing ratio was M=0.5. The results show that if the frequencies of the main flow and the cooling jet flow are increased, the adiabatic centerline effectiveness is decreased and the heat transfer coefficient is increased. Some representative results are: if the frequency of the main flow is increased from 0 Hz to 2 Hz, 16 Hz, or 32 Hz for L/D=1.6, the centerline effectiveness is decreased about 10%, 12%, or 47% and the spanwise-averaged heat transfer coefficient is increased around 1%, 2%, or 4% respectively. If the frequency of the mainstream and the jet flow is increased, the amplitude of the pressure difference between the mainstream and the plenum is increased and the amplitude of coolant flow rate oscillation is increased. Additionally, rectangular or triangular wave forms are used for mainstream and coolant jet flow in order to see the effect on the results and total 36 cases are simulated and effects of changing wave form are investigated. In each case, coolant flow rate was the same as sinusoidal wave forms. It seems like rectangular wave form for main flow at 2 Hz has a negative effect on film cooling performance whereas the same wave form for coolant jet at 32 Hz has a positive effect.

Effects of Oscillations in the Mainstream on Film Cooling at Various Blowing Ratios

2017 ◽  
Author(s):  
Seung Il Baek ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Jet Flow ◽  
Main Flow ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Lift Off

The objective of this study is to understand the effects of flow oscillations in the mainstream and film cooling jets on film cooling at various blowing ratios (0.5, 0.78, 1.0 and 1.5). These oscillations could be caused by the combustion instabilities. They are approximated in sinusoidal form for the current study. The effects of different frequencies (0, 2, 16, 32 Hz) on film cooling are investigated. Simulations are performed using URANS Realizable k-epsilon and LES Smagorinsky-Lilly turbulence models. The results indicate that if the frequencies of the mainstream and the jet flow are increased at a low average blowing ratio of M = 0.5, the adiabatic film cooling effectiveness is decreased and the heat transfer coefficient is increased due to increased disturbance in jet and main flow interaction with increasing frequency. It was observed that when the frequency of the mainstream and the cooling jet flow is increased at M = 0.5, the amplitude of the pressure difference between the mainstream and the plenum is increased resulting in increased amplitude of coolant flow rate oscillations leading to more jet lift off and more disturbance in the main flow and coolant interaction. Consequently, adiabatic film cooling effectiveness is decreased and heat transfer coefficient is increased. If the frequency of the mainstream is increased from 0 Hz to 2, 16, or 32 Hz at M = 0.5, the centerline effectiveness is decreased about 10%, 12%, or 47% and the spanwise-averaged Stanton number ratio is increased about 4%, 5%, or 9% respectively. If the frequencies of the main flow and the jet flow are increased at higher blowing ratios of M = 1.0 and 1.5, adiabatic effectiveness is increased and the spanwise-averaged heat transfer coefficient are decreased. Under steady flow conditions jet lift off is generated for these high blowing ratios. If the frequency of the mainstream and the jet flow is increased, the amplitude of coolant jet flow rate oscillation is increased for the same reason as mentioned above for M = 0.5. This leads to less jet lift off during the cycle resulting in more frequent coolant contact with the wall and consequently increased centerline effectiveness as frequency increases. In addition, the entrainment of hot gases underneath the jet doesn’t lead to higher mixing between the hot mainstream and the coolant and this results in decreased heat transfer coefficient. This is also indicated by the turbulent kinetic energy levels. Some representative results are: when the frequency of the main flow is increased from 0 Hz to 2, 16, or 32 Hz at M = 1.0, the centerline effectiveness is increased about 8%, 19%, or 320%. Also, if the oscillation frequency is increased from 2 Hz to 16, or 32 Hz at M = 1.0, the spanwise-averaged Stanton number ratio is decreased around 2%, to 5% respectively. It seems like the cut off point for low and high blowing ratio behavior of cooling jets is around M = 0.78.

Numerical Investigation of Gas Turbine Combustor Liner Film Cooling Slots

2018 ◽  
Author(s):  
Firat Kiyici ◽  
Ahmet Topal ◽  
Ender Hepkaya ◽  
Sinan Inanli
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Surface Temperature ◽  
Gas Turbine ◽  
Film Cooling ◽  
Turbulent Prandtl Number ◽  
Surface Cooling ◽  
Gas Turbine Combustor ◽  
Cooling Effectiveness ◽  
Combustor Liner

A numerical study, based on experimental work of Inanli et al. [1] is conducted to understand the heat transfer characteristics of film cooled test plates that represent the gas turbine combustor liner cooling system. Film cooling tests are conducted by six different slot geometries and they are scaled-up model of real combustor liner. Three different blowing ratios are applied to six different geometries and surface cooling effectiveness is determined for each test condition by measuring the surface temperature distribution. Effects of geometrical and flow parameters on cooling effectiveness are investigated. In this study, Conjugate Heat Transfer (CHT) simulations are performed with different turbulence models. Effect of the turbulent Prandtl Number is also investigated in terms of heat transfer distribution along the measurement surface. For this purpose, turbulent Prandtl number is calculated with a correlation as a function of local surface temperature gradient and its effect also compared with the constant turbulent Prandtl numbers. Good agreement is obtained with two-layered k–ϵ with modified Turbulent Prandtl number.

The Influence of Film Cooling on Emissions for a Low NOx Radial Swirler Gas Turbine Combustor

2001 ◽  
Author(s):  
G. E. Andrews ◽  
M. N. Kim
Keyword(s):  
Mach Number ◽  
Gas Turbine ◽  
Flow Rate ◽  
Film Cooling ◽  
Equivalence Ratio ◽  
Air Flow ◽  
Gas Turbine Combustor ◽  
Cooling Flow ◽  
Full Coverage ◽  
Primary Zone

An experimental investigation was undertaken of the influence on emissions of full coverage discrete hole film cooling of a lean low NOx radial swirler natural gas combustor. The combustor used radial swirler vane passage fuel injection on the centre of the vane passage inlet. The test configuration was similar to that used in the Alstom Power Tornado and related family of low NOx gas turbines. The test conditions were simulated at atmospheric pressure at the flow condition of lean low NOx gas turbine primary zones. The tests were carried out at an isothermal flow Mach number of 0.03, which represents 60% of industrial gas turbine combustor airflow through the swirl primary zone. The effusion film cooling used was Rolls-Royce Transply, which has efficient internal cooling of the wall as well as full coverage discrete hole film cooling. Film cooling levels of 0, 16 and 40% of the primary zone airflow were investigated for a fixed total primary zone air flow and reference Mach number of 0.03. The results showed that there was a major increase in the NOx emissions for 740K inlet temperature and 0.45 overall equivalence ratio from 6ppm at zero film cooling air flow to 32ppm at 40% coolant flow rate. CO emissions increased from 25ppm to 75ppm for the same increase in film cooling flow rate. It was shown that the main effect was the creation of a richer inner swirler combustion with a surrounding film cooling flow that did not mix well with the central swirling combustion. The increase in NOx and CO could be predicted on the basis of the central swirl flow equivalence ratio.

Heat Transfer Coefficient and Film-Cooling Effectiveness on a Gas Turbine Blade Tip

2002 ◽  
Author(s):  
Jae Su Kwak ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Film Cooling ◽  
Rotor Blade ◽  
Pressure Side ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blade Tip

The detailed distributions of heat transfer coefficient and film cooling effectiveness on a gas turbine blade tip were measured using a hue detection based transient liquid crystal technique. Tests were performed on a five-bladed linear cascade with blow down facility. The blade was a 2-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The Reynolds number based on cascade exit velocity and axial chord length was 1.1 × 106 and the total turning angle of the blade was 97.7°. The overall pressure ratio was 1.32 and the inlet and exit Mach number were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. The blade model was equipped with a single row of film cooling holes at both the tip portion along the camber line and near the tip region of the pressure-side. All measurements were made at the three different tip gap clearances of 1%, 1.5%, and 2.5% of blade span and the three blowing ratios of 0.5, 1.0, and 2.0. Results showed that, in general, heat transfer coefficient and film effectiveness increased with increasing tip gap clearance. As blowing ratio increased, heat transfer coefficient decreased, while film effectiveness increased. Results also showed that adding pressure-side coolant injection would further decrease blade tip heat transfer coefficient but increase film effectiveness.

Gas Turbine Combustor Cooling by Augmented Backside Convection

1979 ◽  
Vol 101 (1) ◽  
pp. 109-115 ◽  
Author(s):  
D. M. Evans ◽  
M. L. Noble
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Cooling System ◽  
Exhaust Gas ◽  
Confined Space ◽  
Gas Turbine Combustor ◽  
Exhaust Gas Emission ◽  
Cooling Air ◽  
Cooling Methods

Traditionally, gas turbine combustor walls have been cooled by one or more of the various film cooling methods. The current motivation to control exhaust gas emission composition has led to the serious consideration of backside convection wall cooling, where the cooling air is introduced to the main gas stream not prior to the dilution zone. Due to the confined space and the severe nature of the wall cooling problem, it is essential to maximize the heat transfer/pumping power characteristic, which suggests an augmented convection technique. A particular heat transfer design of a combustor cooled by means of transverse rib turbulence promoters applied to the exterior wall of the annular spaces surrounding the primary and secondary zones is described. Analytical methods for designing such a cooling system are reviewed and a comparison between analytical and experimental results is presented.

Effect of Unsteady Wake on Detailed Heat Transfer Coefficient and Film Effectiveness Distributions for a Gas Turbine Blade

1997 ◽  
Author(s):  
Hui Du ◽  
Je-Chin Han ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Gas Turbine ◽  
Film Cooling ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Nusselt Numbers ◽  
Unsteady Wake ◽  
Cooled Blade

Unsteady wake effects on detailed heat transfer coefficient and film cooling effectiveness distributions from a gas turbine blade with film cooling are obtained using a transient liquid crystal technique. Tests were performed on a five-blade linear cascade at a axial chord Reynolds number of 5.3 × 105 at cascade exit. Upstream unsteady wakes are simulated using a spoke-wheel type wake generator. The test blade has three rows of film holes on the leading edge and two rows each on the pressure and suction surfaces. Air and CO2 were used as coolants to simulate different coolant-to-mainstream density ratio effect. Coolant blowing ratio for air injection is varied from 0.8 to 1.2 and is varied from 0.4 to 1.2 for CO2. Results show that Nusselt numbers for a film-cooled blade are much higher compared to a blade without film injection. Particularly, film injection causes earlier boundary layer transition on the suction surface. Unsteady wakes slightly enhance Nusselt numbers but significantly reduce film cooling effectiveness on a film-cooled blade compared with a film-cooled blade without wakes. Nusselt numbers increase slightly but film cooling effectiveness increases significantly with an increase in blowing ratio for CO2 injection. Higher density coolant (CO2) provides higher effectiveness at higher blowing ratios (M = 1.2) whereas lower density coolant (Air) provides higher effectiveness at lower blowing ratios (M = 0.8).

Numerical Investigation of Heat Transfer Enhancement in Gas Turbine Blade by Air Film Cooling and Different Types of Ribs

2013 ◽  
Author(s):  
Maryam Pourhasanzadeh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Film Cooling ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Convection Heat Transfer Coefficient ◽  
The Heat Transfer Coefficient

In this research, numerical studies have been carried out for a film cooling jet on a gas turbine blade in the presence of different kinds of ribs. Simulations are performed for a film cooling jet inclined at 30-degrees. The effect of coolant jet velocity on convection heat transfer coefficient (h) is investigated. In addition, various ribs geometries and their distance from the blade surface are examined. It is shown that a combination of the rib and the film cooling jet stimulate the momentum and thermal boundary layers and subsequently improve the convection heat transfer coefficient. It is indicated that the heat transfer coefficient is dependent on the height of the rib and there is an inverse relation with the rib distance from the plate. Moreover, an increase in coolant jet velocity causes the increase of the heat transfer coefficient. The results show a significant improvement of the heat transfer coefficient over three times more than h on a blade without any ribs or coolant jet.

Numerical Investigations on the Heat Transfer Performance of Transonic Squealer Tip With Different Film Cooling Layouts

2020 ◽  
Author(s):  
Shijie Jiang ◽  
Zhigang Li ◽  
Jun Li ◽  
Liming Song
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Film Cooling ◽  
High Speed ◽  
Thermal Stresses ◽  
High Heat ◽  
Tip Leakage Flow ◽  
High Heat Transfer

Abstract Tip leakage flow in high speed turbine induce significant thermal loads and give rise to intense thermal stresses on blade tip, while increasing inlet pressure tends to accelerate leakage velocity beyond transonic regime. The present research quantifies heat transfer and film cooling effect on a squealer tip with three film cooling layouts, three coolant mass flow rates and a relative casing movement. The results indicate that area-averaged HTC of PS layout is higher than that of CAM layout by 6.9% and that of SS layout by 5.7% when coolant flow rate equals to 0.6% mainstream flow rate. By comparison, it is clearly observed that area of the high heat transfer coefficient regions are significantly enlarged when the flow rate of coolant is increased. With relative casing movement, a significant high HTC stripe parallel to pressure side rim is formed. In case of the PS layout, heat transfer coefficient is reduced by 7.3% with casing movement. While in case of CAM layout and SS layout, heat transfer coefficient increased by 4.8% and 2.3% with casing movement, respectively. Detailed flow patterns with three film cooling layouts are also illustrated.

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