Italy 2014ugm Heat Transfer Enhancement

8/10/2019 Italy 2014ugm Heat Transfer Enhancement

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HEAT TRANSFER ENHANCEMENT DUE TO

COOLANT EXTRACTION ON THECOLD SIDE OF EFFUSION COOLING PLATES

Riccard o Da Sog he, A . A nd reini , B. Facch ini and L. Mazzei

Ergon Research s.r.l .Via Panciatichi, 92 - 50139

Florence (Italy)e-mail:

[email protected]


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Presentation Outline

Introduction Effusion cooling arrangement

Reasons and objectives of the present work

CFD computations CFD setup Test matrix Validation of numerical tools Results

Conclusions


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Introduction

ACARE Vision 2020 objectives and future ICAO-CAEP standards specifically

introduce NO x emission abatement as one of the main goals for nextgeneration civil aero-engines Research efforts dedicated to the introduction of lean premixed

combustion systemsRepresent the most effective way to reach the NO x reductiontargets

The design of the liner cooling system which becomes morecritical

Up to 70% of the overall air mass flow is utilized for fuelpreparation and the initiation of lean combustion

Goal in combustor development Significant reduction of the amount of coolant

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Introduction: Effusion cooling arrangement

High efficiency cooling scheme Effusion cooling

Huge number of small holesRecent improvements of drilling capabilityHighly innovative potential

Promising acoustic damping capabilities More uniform film protection of the

liner hot side

Significant heat sink effectHeat removed by convection inside holes

Relevant heat extraction by the cold sideconvection cooling

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Avio NEWAC Lean Burn Combustor GT2013-94667

Courtesy of Paradigm precisionCourtesy of Paradigm precision


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Introduction: Previous literature contributions

Hot side heat transfer

Pioneering works from Sasaki et al. (1979), Mayle and Camarata (1975), Andrews (1990, 1991, 1995) Recent works about effectiveness and heat transfer measurements on

effusion cooling systems Papers from Scrittore et. al. (2005, 2006) as well as the recent work of Ligrani

et. al. (2012) and Martin and Thorpe (2012) report detailed description of theeffect of blowing ratio in large arrays of full coverage film cooling geometriesRange of engine representative blowing ratiosNumber of rows to obtain a full developed filmIncrease of film effectiveness at higher BRs when considering high free streamturbulence

Paper from Andreini et. al. (2013) investigates adiabatic and overalleffectiveness of effusion cooling plates at different operating conditions

A correlation for overall effectiveness by the effusion geometries proposedto help preliminary assessment of different design solutions

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Cold side heat transfer

Gerendas and co-workers (2001) pointed out that in case of effusioncooling up to 30% of the heat extracted from the liner is due to cold sideconvective cooling

This evidence is explained by a heat transfer augmentation at the extraction

holes entranceSparrow et. al (1982), Cho et. al (1987) and Dorignac (2005): The heat transfercoefficient augmentation at the liner cold side is motivated by stagnation regionsobserved downstream the extraction holes

The heat transfer coefficient enhancement factor EF depends on the suction ratio SR

=

These studies focused on isolated extraction holes

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Cold side heat transfer

Cottin et al. (2011) numerically investigate the aero-thermal field ofeffusion cooling plates.

The authors pointed out an expression to correlate the cold side heattransfer coefficient augmentation to the local suction ratio.

The coefficients of this correlation were not publishedThe impact of the hole spacing as well as the operating conditions of the system arenot accounted for.The flow approaching the effusion plate is modelled as fully developed.

Correlations for the effusion plate cold side heat transferenhancement factor as a function of plate porosity and real engine

operating condition are NOT available in the open literature

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Aim of the work

Analyze, by means of CFD, the flow field on the cold side of effusioncooling plates when considering 30 angled perforations

Both geometrical and fluid-dynamic design parameters are considered toimprove the physical understanding of the fluid flow that characterizethese devices

Effusion plate porosity Feeding channel Reynolds number Pressure ratio across the plate Turbulence intensity

Develop a correlation for the htc enhancement factor as afunction of both plate porosity and operating conditions

Reasons and objectives

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Ansys CFX-14.0 Steady state solutions, ideal gas

Numerical domain 18 cooling holes rows

Turbulence modeling k- SST

Low Reynolds approach

Gamma-Theta transition model Boundary conditions

Feeding channel inletPlug flow (uniform velocity)Total TemperatureTurbulence intensity and length scale

Feeding channel outletStatic pressure

Discharge PlenumOpening condition (Pressure)

WallsFixed Temperature

CFD solver setup

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Geometries Plate porosity

1.16%1.82%2.84%

Operating conditions

Feeding channel Reynolds number250000 750000

Pressure ratio 1.005 1.05

Turbulence intesity32% 16%

Test matrix

10

=0.25


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Validation of numerical setup

Holes discharge coefficient Experimental data from Gritsch and co-workers (2001)

11

=


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Heat transfer coefficient Experimental data from Byerley (1989)

Single extraction hole arrangement The numerical domain mimics the experimental test rig

The comparisons are done in term of Enhancement Factor EF

= where = 0.021 . .

Both line lateral averaged and area averaged profiles are considered

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Line lateral average Area average surface


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Line-averaged Enhancement Factor profiles Sensitivity to mesh refinement

Three different meshes are compared These grids were generated changing the global scale factor of 25% and +25% and hence halving and

doubling the number of elements

Mesh independence is achieved when considering the standard grid

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Sensitivity to turbulence model Standard k- SST vs k- SST -Re t

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EF peak is always achieved at thedownstream hole edge The effects of flow extraction is

relevant up to 8 hole diametersdownstream

Fully turbulent simulations over-predictthe EF significantly

Accordingly with Byerlay (1989) theboundary layer downstream the

extraction hole presents a transitionalbehavior

The k- SST -Re t improves theagreement between the CFD andthe experiments significantly

L i n e - a v e r a g e

d

A r e a - a v e r a g e

d


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Results

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Post-processing and scaling procedure

For each hole, three entities have been created A triangle-shaped plane long 2 S x and wide S y /2, where htc and EF are area averaged A plane located in correspondence of the hole and normal to the flow, where Re, Pr,

Vfeeding channel and T 0,bulk are calculated A plane located within the hole, where V hole is calculated

The heat transfer coefficient and the EF are calculated as follow:

=

, ; =

0 = 0.0243 . .

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Results: Effects of Pressure Ratio =1.16, Re=550k, Tu=32%

The pressure ratio across the plate affects significantly the Enhancement Factor As the pressure ratio increase the EF parameter increase

Increase of leads to an increase of SR

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The enhancement factor slightlydecreases moving from thefeeding channel inlet to its exit

The decreasing rate is more evident at thefirst holes of the array

The EF trend becomes roughly flat whenapproaching the effusion plate exit


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Results: Effects of Pressure Ratio =1.16, Re=550k, Tu=32%

The enhancement factor slightly decreases moving from the feeding channel inletto its exit

This behavior is motived by the interplay of the eddy viscosity trend and the suction ratio trendThe eddy viscosity decrease due to both the holes bleeding and the walls presenceThe SR increases due to the perforations bleeding

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Results: Effects of Reynolds number and Turbulence intensity =1.16, =1.05

The feeding channel Reynolds numberhas a weak impact on the EF

As the Re decreases the EF slightincreases

Confirms what observed in case ofisolated holes (Byerlay (1989), Andreiniet al. (2014))

The increase of the turbulence levelleads to an higher enhancement factor The effect of the turbulence level on the

EF is modest

A reduction of Tu by 50% involves areduction of EF by 6%

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Results: Effects of effusion plate porosity Re=550K, =1.05, Tu 32%

The Enhancement Factor is quiteaffected by the effusion plate

porosity

As the increases, EF increases The EF averaging procedure considers

surfaces closest to the holes leading tohigher EF mean levels

EF levels very close to the effusion holesinlet are not influenced so much by the parameter

As the plate porosity increases, the EFdecays from the peak value to itsminimum in a smoother way

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Results: Effects of effusion plate porosity Re=550K, =1.05, Tu 32%

As increases, the EF decays in asmoother way

As increases more mass flow rate perunit length is collected close to theholes region

The higher velocity component normalto the wall results in a thinner boundarylayer enhancing the heat transfer

process

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Results: CFD data reduction The Enhancement Factor is expressed as function of the Pressure ratio

across the plate and its porosity

= 5.73 + 0.89 + 5.41 + 0.135

Mean error 4.8% Std. Deviation 3%

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Conclusions

A three dimensional CFD analysis was performed in order to investigate the heattransfer at the cold side of effusion plates Both geometrical and fluid-dynamic design parameters have been considered

Extraction holes spacing both in streamwise and spanwise direction leading to porosity factorstypically implemented on real engines

The CFD setup has been extensively validated by means the experimental data providedby Byerley (1989) and by Gritsch et. al

The validation campaign shows that the CFD is able to confidently catch the EF

The analysis pointed out that: The effects of both feeding channel Reynolds number and the turbulence intensity at the

inlet of the cooling section, have a weak effect on the enhancement factor An empirical correlation for the prediction of the cold side heat transfer coefficient

enhancement factor EF has been proposed:It expresses the EF related to each extraction hole as a function of the pressure ratio and theeffusion plate porosity factor

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HEAT TRANSFER ENHANCEMENT DUE TO

COOLANT EXTRACTION ON THECOLD SIDE OF EFFUSION COOLING PLATES

Riccard o Da Sog he, A . A nd reini , B. Facch ini and L. Mazzei

Ergon Research s.r.l .Via Panciatichi, 92 - 50139

Florence (Italy)e-mail:

[email protected]

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Italy 2014ugm Heat Transfer Enhancement

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