The Delta Phi Method of Evaluating Overall Film Cooling Performance

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
David G. Bogard
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
Metal Temperature ◽  
Edge Region ◽  
Adiabatic Wall ◽  
Constant Wall Temperature ◽  
Cooling Performance

Film cooling designs are often evaluated experimentally and characterized in terms of their spatial distributions of adiabatic effectiveness, η, which is the nondimensionalized form of the adiabatic wall temperature, Taw. Additionally, film cooling may alter the convective heat transfer coefficient with the possibility of an increase in h that offsets the benefits of reduced Taw. It is therefore necessary to combine these two effects to give some measure of the benefit of film cooling. The most frequently used method is the net heat flux reduction (NHFR), which gives the fractional reduction in heat flux that accompanies film cooling for the hypothetical case of constant wall temperature. NHFR is imperfect in part due to the fact that this assumption does not account for the primary purpose of film cooling—to reduce the metal temperature to an acceptable level. In the present work, we present an alternative method of evaluating film cooling performance that yields the reduction in metal temperature, or in the nondimensional sense, an increase in ϕ that would be predicted with film cooling. This Δϕ approach is then applied using experimentally obtained η and h/h0 values on a simulated turbine blade leading edge region. The delta-phi approach agrees well with the legacy NHFR technique in terms of the binary question of whether the film cooling is beneficial or detrimental, but provides greater insight into the temperature reduction that a film cooling design would provide an actual turbine component. For example, instead of giving an area-averaged NHFR = 0.67 (indicating a 67% reduction in heat flux through film cooling) on the leading edge region with M = 0.5, the Δϕ approach indicates an increase in ϕ of 0.061 (or a 61 K surface temperature decrease with a notional value of T∞ −Tc = 1000 K). Alternatively, the technique may be applied to predict the maximum allowable increase in T∞ against which a film cooling scheme could protect.

The Delta Phi Method of Evaluating Overall Film Cooling Performance

2015 ◽  
Author(s):  
James L. Rutledge ◽  
Marc D. Polanka ◽  
David G. Bogard
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
Metal Temperature ◽  
Edge Region ◽  
Adiabatic Wall ◽  
Constant Wall Temperature ◽  
Cooling Performance

Film cooling designs are often evaluated experimentally and characterized in terms of their spatial distributions of adiabatic effectiveness, η, which is the nondimensionalized form of the adiabatic wall temperature, Taw. Additionally, film cooling may alter the convective heat transfer coefficient with the possibility of an increase in h that offsets the benefits of reduced Taw. It is therefore necessary to combine these two effects to give some measure of the benefit of film cooling. The most frequently used method is the net heat flux reduction, which gives the fractional reduction in heat flux that accompanies film cooling for the hypothetical case of constant wall temperature. NHFR is imperfect in part due to the fact that this assumption does not account for the primary purpose of film cooling — to reduce the metal temperature to an acceptable level. In the present work we present an alternative method of evaluating film cooling performance that yields the reduction in metal temperature, or in the nondimensional sense, an increase in ϕ that would be predicted with film cooling. This Δϕ approach is then applied using experimentally obtained η and h/h0 values on a simulated turbine blade leading edge region. The delta-phi approach agrees well with the legacy NHFR technique in terms of the binary question of whether the film cooling is beneficial or detrimental, but provides greater insight into the temperature reduction that a film cooling design would provide an actual turbine component. For example, instead of giving an area-averaged NHFR = 0.67 (indicating a 67% reduction in heat flux through film cooling) on the leading edge region with M = 0.5, the Δϕ approach indicates an increase in ϕ of 0.061 (or a 61 K surface temperature decrease with a notional value of T∞ - Tc = 1000 K). Alternatively, the technique may be applied to predict the maximum allowable increase in T∞ against which a film cooling scheme could protect.

scholarly journals An Investigation of Treating Adiabatic Wall Temperature as the Driving Temperature in Film Cooling Studies

2011 ◽  
Author(s):  
Lei Zhao ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Wall Temperature ◽  
Film Cooling ◽  
Injection Hole ◽  
Adiabatic Wall ◽  
Temperature Potential ◽  
Driving Potential

In film cooling heat transfer analysis, one of the core concepts is to deem film cooled adiabatic wall temperature (Taw) as the driving potential for the actual heat flux over the film-cooled surface. Theoretically, the concept of treating Taw as the driving temperature potential is drawn from compressible flow theory when viscous dissipation becomes the heat source near the wall and creates higher wall temperature than in the flowing gas. But in conditions where viscous dissipation is negligible, which is common in experiments under laboratory conditions, the heat source is not from near the wall but from the main hot gas stream; therefore, the concept of treating the adiabatic wall temperature as the driving potential is subjected to examination. To help investigate the role that Taw plays, a series of computational simulations are conducted under typical film cooling conditions over a conjugate wall with internal flow cooling. The result and analysis support the validity of this concept to be used in the film cooling by showing that Taw is indeed the driving temperature potential on the hypothetical zero wall thickness condition, ie. Taw is always higher than Tw with underneath (or internal) cooling and the adiabatic film heat transfer coefficient (haf) is always positive. However, in the conjugate wall cases, Taw is not always higher than wall temperature (Tw), and therefore, Taw does not always play the role as the driving potential. Reversed heat transfer through the airfoil wall from downstream to upstream is possible, and this reversed heat flow will make Tw > Taw in the near injection hole region. Yet evidence supports that Taw can be used to correctly predict the heat flux direction and always result in a positive adiabatic heat transfer coefficient (haf). The results further suggest that two different test walls are recommended for conducting film cooling experiments: a low thermal conductivity material should be used for obtaining accurate Taw and a relative high thermal conductivity material be used for conjugate cooling experiment. Insulating a high-conductivity wall will result in Taw distribution that will not provide correct heat flux or haf values near the injection hole.

THE DUFOUR EFFECT IN FILM COOLING EXPERIMENTS WITH FOREIGN GASES

2021 ◽  
pp. 1-17
Author(s):  
James L. Rutledge ◽  
Carol Bryant ◽  
Connor Wiese ◽  
Jacob Anthony Fischer
Keyword(s):  
Wall Temperature ◽  
Film Cooling ◽  
Leading Edge ◽  
Temperature Gradients ◽  
Coolant Temperature ◽  
Adiabatic Wall ◽  
Dufour Effect ◽  
Temperature Separation ◽  
Thermal Conductivity Model ◽  
Cooling Hole

Abstract In typical film cooling experiments, the adiabatic wall temperature may be determined from surface temperature measurements on a low thermal conductivity model in a low temperature wind tunnel. In such experiments, it is generally accepted that the adiabatic wall temperature must be bounded between the coolant temperature and the freestream recovery temperature as they represent the lowest and highest temperature introduced into the experiment. Many studies have utilized foreign gas coolants to alter the coolant properties such as density and specific heat to more appropriately simulate engine representative flows. In this paper, we show that the often ignored Dufour effect can alter the thermal physics in such an experiment from those relevant to the engine environment that we generally wish to simulate. The Dufour effect is an off-diagonal coupling of heat and mass transfer that can induce temperature gradients even in what would otherwise be isothermal experiments. These temperature gradients can result in significant errors in calibration of various experimental techniques, as well as lead to results that at first glance may appear non-physical such as adiabatic effectiveness values not bounded by zero and one. This work explores Dufour effect induced temperature separation on two common cooling flow schemes, a leading edge with compound injection through a cylindrical cooling hole, and a flat plate with axial injection through a 7-7-7 shaped cooling hole. Air, argon, carbon dioxide, helium, and nitrogen coolant were utilized due to their usage in recent film cooling studies.

Influence of Film Cooling Unsteadiness on Turbine Blade Leading Edge Heat Flux

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
James L. Rutledge ◽  
Paul I. King ◽  
Richard B. Rivir
Keyword(s):  
Heat Flux ◽  
Turbine Blade ◽  
Film Cooling ◽  
Flow Behavior ◽  
Leading Edge ◽  
Coolant Flow ◽  
Adiabatic Wall ◽  
Stagnation Line ◽  
Turbine Engine ◽  
Cooling Flow

Film cooling in the hot gas path of a gas turbine engine can protect components from the high temperature main flow, but it generally increases the heat transfer coefficient h partially offsetting the benefits in reduced adiabatic wall temperature. We are thus interested in adiabatic effectiveness η and h which are combined in a formulation called net heat flux reduction (NHFR). Unsteadiness in coolant flow may arise due to inherent unsteadiness in the external flow or be intentionally introduced for flow control. In previous work it has been suggested that pulsed cooling flow may, in fact, offer benefits over steady blowing in either improving NHFR or reducing the mass flow requirements for matched NHFR. In this paper we examine this hypothesis for a range of steady and pulsed blowing conditions. We use a new experimental technique to analyze unsteady film cooling on a semicircular cylinder simulating the leading edge of a turbine blade. The average NHFR with pulsed and steady film cooling is measured and compared for a single coolant hole located 21.5° downstream from the leading edge stagnation line, angled 20° to the surface and 90° to the streamwise direction. We show that for moderate blowing ratios at blade passing frequencies, steady film flow yields better NHFR. At higher coolant flow rates beyond the optimum steady blowing ratio, however, pulsed film cooling can be advantageous. We present and demonstrate a prediction technique for unsteady blowing at frequencies similar to the blade passing frequency that only requires the knowledge of steady flow behavior. With this important result, it is possible to predict when pulsing would be beneficial or detrimental.

Net Heat Flux Reduction and Overall Effectiveness for a Turbine Blade Leading Edge

2005 ◽  
Author(s):  
Brian D. Mouzon ◽  
Elon J. Terrell ◽  
Jason E. Albert ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Film Cooling ◽  
Leading Edge ◽  
Cooling Performance ◽  
Net Heat Flux ◽  
Laboratory Models ◽  
Overall Effectiveness ◽  
Blade Leading Edge

The external cooling performance of a film cooled turbine airfoil can be quantified as a net reduction in heat transfer relative to the turbine airfoil without film cooling. This quantification is generally accomplished by using measurements of the adiabatic effectiveness and the change in heat transfer coefficients (hf/h0) for the film cooled surface to determine the net heat flux reduction (Δqr). Although measurement of Δqr for laboratory models give an indication of the ultimate film cooling performance, this does not show how much the surface temperature of the airfoil is reduced by film cooling. Measurement of scaled surface temperatures can be accomplished by using laboratory models constructed so that the Biot number is matched with that of the actual airfoil. These measurements provide a scaled temperature distribution on the airfoil that is referred to as the overall effectiveness, φ. For the current study, measurements of Δqr and φ have been made for a simulated turbine blade leading edge. The simulated leading edge incorporated shaped coolant holes, and had three rows of coolant holes. Improvements due to the shaped holes were determined by comparisons with previously measured round hole configurations. Spatially distributed hf/h0 show increases of 5% to 15% for M = 1.0 and 10% to 30% for M = 2.0. Results show that local variation in Δqr much greater than variation in φ, but laterally averaged Δqr distributions are reasonable predictors of the laterally averaged φ distributions.

Numerical Study on Aero-Thermal Performance of HP Turbine Endwalls Under Influence of Hot Streak and High Mainstream Turbulence

2016 ◽  
Author(s):  
Zhiduo Wang ◽  
Wenhao Zhang ◽  
Zhaofang Liu ◽  
Chen Zhang ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbulence Intensity ◽  
Wall Temperature ◽  
Numerical Study ◽  
Leading Edge ◽  
Heat Transfer Characteristics ◽  
Adiabatic Wall ◽  
Transfer Characteristics ◽  
Hot Streak

In this paper, unsteady RANS simulations were performed at two hot streak (HS) circumferential positions with inlet turbulence intensity of 5% and 20%. The interacted HS and high mainstream turbulence effects on endwall heat transfer characteristics of a high-pressure (HP) turbine were discussed by analyzing the flow structures and presenting the endwall adiabatic wall temperature, heat transfer coefficient (HTC) and heat flux distributions. The results indicate that both the wall temperature and HTC increase with the turbulence intensity at most stator endwall regions. In addition, the increase of wall temperature plays a greater role than HTC of influencing the wall heat flux. However, higher turbulence intensity decreases the intensity of the stator passage horse-shoe vortex, also the corresponding region HTC and heat flux are reduced. In rotor passage, the variation of HS circumferential position would alter the hub and casing endwall temperature, however, the discrepancy is weakened at higher turbulence. The elevated HS attenuation at higher turbulence results in temperature augmentation at the leading edge of rotor hub and casing endwalls, while temperature decrease after 50% axial chord, thus obtains more uniform temperature distributions on the endwalls. However, the rotor endwall HTC is only augmented significantly at the leading edge on hub endwall, and pressure side and downstream of trailing edge on casing endwall. Variation of HTC and adiabatic wall temperature jointly determines the rotor hub and casing endwall heat flux, and the temperature variation has dominant effects in the most regions. In general, the variation of adiabatic wall temperature and HTC should be considered simultaneously when analyzing the turbine endwall heat transfer characteristics.

Analysis of the Heat Transfer Driving Parameters in Tight Rotor Blade Tip Clearances

2014 ◽  
Author(s):  
S. Lavagnoli ◽  
C. De Maesschalck ◽  
G. Paniagua
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Tip Clearance ◽  
Adiabatic Wall ◽  
Engine Operation ◽  
Flow Parameters

Turbine rotor tips and casings are vulnerable to mechanical failures due to the extreme thermal loads they undergo during engine operation. In addition to the heat flux variations during the transient phase, high-frequency unsteadiness occurs at every rotor passage, with amplitude dependent on the tip gap. The development of appropriate predictive tools and cooling schemes requires the precise understanding of the heat transfer mechanisms. The present paper analyzes the nature of the overtip flow in transonic turbine rotors running at tight clearances, and explores a methodology to determine the relevant flow parameters that model the heat transfer. Steady-state three-dimensional Reynolds-Averaged Navier-Stokes calculations were performed to simulate engine-like conditions considering two rotor tip gaps, 0.1% and 1% of the blade span. At tight tip clearance, the adiabatic wall temperature is not anymore independent of the solid thermal boundary conditions. The adiabatic wall temperature predicted with the linear Newton’s cooling law was observed to rise to non-physical levels in certain regions within the rotor tip gap, resulting in unreliable convective heat transfer coefficients. This paper investigates different approaches to estimate the relevant flow parameters that drive the heat transfer. The present study allows experimentalists to retrieve information on the gap flow temperature and convective heat transfer coefficient based on the use of wall heat flux measurements. Such approach is required to improve the accuracy in the evaluation of the heat transfer data while enhancing the understanding of tight-clearance overtip flows.

scholarly journals Computation of Full-Coverage Film-Cooled Airfoil Temperatures by Two Methods and Comparison With High Heat Flux Data

1987 ◽  
Author(s):  
H. J. Gladden ◽  
F. C. Yeh ◽  
P. J. Austin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Convective Heat Transfer Coefficient ◽  
Superposition Method ◽  
High Heat Flux ◽  
Adiabatic Wall ◽  
Full Coverage

Two methods were used to calculate the heat flux to full-coverage film cooled airfoils and, subsequently, the airfoil wall temperatures. The calculated wall temperatures were compared to measured temperatures obtained in the Hot Section Facility operating at real engine conditions. Gas temperatures and pressures up to 1900 K and 18 atm with a Reynolds number up to 1.9 million were investigated. Heat flux was calculated by the convective heat transfer coefficient adiabatic wall method and by the superposition method which incorporates the film injection effects in the heat transfer coefficient. The results of the comparison indicate the first method can predict the experimental data reasonably well. However, superposition overpredicted the heat flux to the airfoil without a significant modification of the turbulent Prandtl number. The results of this research suggests that additional research is required to model the physics of full-coverage film cooling where there is significant temperature/density differences between the gas and coolant.

Heat Transfer Analysis Over a Film Cooled Platform of a Vane Cascade With a Non-Uniform Inlet Flow

2017 ◽  
Author(s):  
G. Barigozzi ◽  
S. Ravelli ◽  
H. Abdeh ◽  
A. Perdichizzi ◽  
M. Henze ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Film Cooling ◽  
Cooling System ◽  
Convective Heat Transfer Coefficient ◽  
Leading Edge ◽  
Heat Transfer Analysis ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Inlet Flow Distortion

This paper reports on heat transfer measurements performed on the film cooled platform of a linear nozzle vane cascade, subject to non-uniform inlet flow conditions. An obstruction, installed upstream of the cascade at different tangential positions, was responsible for inlet flow distortion. The platform cooling system included both purge flow from a slot located upstream of the leading edge and coolant ejection from a row of cylindrical holes located upstream of the slot. Testing was performed at inlet Mach number of Ma1 = 0.12 with both slot and combustor holes blowing at nominal conditions. Measured values of adiabatic film cooling effectiveness on the platform were used to obtain a detailed map of the convective heat transfer coefficient. The final goal was to compute the net heat flux reduction (NHFR), due to film cooling, when varying the relative position between obstruction and airfoil. Aligning the inflow non uniformity with the vane leading edge leads to a detrimental increase in the heat flux into the platform, within the vane passage. Conversely, positive NHFR values are observed over most of the platform surface if the inlet flow distortion is moved toward the suction side of the adjacent vane.

Hole arrangement effect to film cooling performance on leading edge region of rotating blade

2021 ◽  
Vol 169 ◽  
pp. 107034
Author(s):  
Gang Xie ◽  
Zhi Tao ◽  
Zhi-yu Zhou ◽  
Ru-quan You ◽  
Shuang-zhi Xia ◽  
...  
Keyword(s):  
Film Cooling ◽  
Leading Edge ◽  
Edge Region ◽  
Cooling Performance ◽  
Rotating Blade
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