internal cooling of a hot turbine structure - lth · internal cooling of a hot turbine structure...

Internal Cooling of a Hot Turbine Structure

Zahra Ghorbani-TariDivision of Heat Transfer, Department of Energy Sciences

Lund University

Lund University/LTH/ Energy Sciences/ Heat Transfer /091202

Part 1 : Introduction

Part 2 : Calibration of wide-band LCStrategy of calibrationResult

HT measurement in smooth channel flowPreparation of test sectionMethodologyResult

Concluding remark

Part 3: Next step in HT measurements

Presentation Layout

Lund University/Dept. Energy Sciences/ Div. Heat Transfer /091202

Introduction

TMS are used in turbofan engines to guide the flow from the short-radius HPT to the large-radius LPT.

Typical turbofan (GP7000) engine with 4 sectionsTurbine section: High pressure turbine (HPT),Turbine Mid Structure (TMS), Low pressure turbine (LPT)

Lund University/Dept. Energy Sciences/ Div. Heat Transfer /091202

Introduction

Problem statement:TMS is located downstram of the HPT and it is exposed to very high heat loads.Cooling is needed to avoid leakage from the hot gas channel intothe domain surrounding the cold load carrying struture

Channel inlet

Leakage

The right the swirl flow with curved channel, ribs and jet injection.

outlet

Turbine section: HPT,TMS, LPT


Basic approach & scope

Build a rather simple and easily changeable test rig (in HP stage cooling) Channel inlet

Curved channel flow

Jet injection

Rib

outlet

Flows of interest for cooling:

- Injection effects : feeding single/double confined jet- Surface disturbances: cylinder

ribs


Objectives

To investigate :

Forced convective heat transferTurbulent flow

2 measurement techniques applied:

Liquid crystal thermography (LCT)Particle image velocimetry (PIV)


Calibration of Wide-band Thermochromic Liquid Crystal (TLC R35C10W)

Part 2.1

ObjectiveTo demonstrate broader portion heat transfer distribution on thesurface in the channel flow combined with injection jet (s),multiple ribs, etc


Liquid Crystal Thermography

TLC response to heating

PropertyThermochromic liquid crystal (TLC) change colors in response to temperature changes.ApplicationWhen TLC surface is illuminated with a white light source and heated through an active temperature range, it exhibits colors from red to blue through the visible color spectrum. This behavior is repeatable and reversible so that the TLC color can be calibrated directly as a function of temperature .

R35C10WLC with an event temperature 35 °C and color bandwidth of 10 °C.- Below event temperature, the LC appears transparent.- T rises through the bandwidth, LC turns R, G, and Bsequentially. - T exceeds the clearing point, LC reverts back to being transparent.


Color interpretation

RGB ( red, green and blue)RGB defines a color

Human eye can not resolve the components of a color mixture

HSI ( Hue, saturation and intensity)HSI uses RGB concept to describe a color.

Hue- colorSaturation- purity of the colorIntensity- brightness of the color

Purple color is a mix of 56% red, 5% green, 61% blue


Hue technique

In applications, R, G, B components of the image matrix are converted into H, S, I components.

Hue is directly related to the temperature

The relationship between hue and temperature is monotonic and hue is thus calibrated versus temperature.

Hue-temperature calibration curve is used to demonstrate the surface temperature distribution on the inner wall of the duct.


Physical form : polyester sheet (Thin film of LC sandwiched between a transparent polymer substrate sheet and a black absorbing background)

Apparatus- 5 calibrated K-type thermocouples as reference to

calibrate LC.- Ordinary fluorescent lamp as a primary illuminant .- Image acquisition and software for image analysis

(CCD camera, PC, software, etc.)

Summary of Calibration


- Steady state calibration technique (TLC is set to pre-determined temperature within the color bandwidth and the image of the surface is acquired. The process is repeated through the bandwidth)

Pay efforts to capture images in steps of 0.5°C through the entire bandwidth.

-The calibration was conducted in situ, keeping identical optical arrangements as in the experiments.

Calibration Strategy


Result: calibration curve

R35C5W hue-temperature feature

- The curve is fairly linear in the range of 35 °C to 37 °C.- The effective temperature range would be from 35 °C to 37 °C. - Resolution is 0.02 °C.

- Hue has a considerable sensitivity in the range of 36 °C to 41°C. - The effective temperature range would be the from 36°C to 43 °C .- Resolution is 0.1 °C .



Part 2.2

Heat Transfer Measurement in Smooth Duct


Test Rig

Downstream look towards the fan Air intake Suction fan

Test section, flexible walls


Dimension of Thermal Rig

Inlet plane

Test section

Flow monitoring holes, top and side

Fan

Intake

3 m

1 m 1 m

inlet

250 [mm], wall S1

250 [mm], wall S2

250 [mm], wall S3

250 [mm], wall S480 [mm]

320 [mm]

outlet

Thermal test section

Heat transfer measurement is performed at the location of 3 m from the inlet duct where thermal B.L is fully developed.


Heat foils

Liquid crystal strips

Sector 1

Sector 2

Sector 3

Sector 4

LC strips

Heating foil

LCT configuration ; S2 & S3

LCT configuration

Preparation: Thermal section (1)

Only one broader wall of the duct is electrically heated and the others are adiabatic.

LC strips are covered on the broader wall of the test section to demonstrate wall temperature distribution.


CCD

Lights

Thermal section

Adjust : illumination of primary lightsCCD camera

Primary disturbances:- Reflections from heating foil- Shades from different sources

Covering test window by a dark enclosure to prevent the interferencesfrom surrounding light

Preparation: Thermal section (2)

Thermal test section


Test 1:HT measurements in Smooth Channel

Objective To measure the heat transfer (in terms of Nu) over the whole LC strip within the bandwidth in the measurement region:

Re = 10k-100k

Theory: Nu calculated from the Dittus-Boelter correlation with symmetric heating (1) and asymmetric heating correlation (2) :

Nu H = 0.023 Re H0.8. Pr 0.4 (1)

Nu H = 0.041 Re H0.727(2)

Experiment: Nu measured directly from heat flux and temperature difference:

Heat foil

TLC

Measurement region

A: area of heating surface (m2)kf : air thermal conductivity (W/m.K)

H: height of channel flow (m)

( )( ) AkTT

HQQNufbulkw

lossel

...

−−

=

νHum

H.Re =

Q el: measured input power to heater (W/m2)Q loss: heat loss by conduction (W/m2) Tbulk : air bulk temperature (K)Tw : surface temperature indicated by LC (K )


Result: Re=10k‐100kExperimental condition : the temperature difference between surface and air bulk was kept within 13-15 °C.

Nusselt number in smooth duct

The consistency of the measured Nu with asymmetric heating correlation is clearly concluded.


Figure shows Nu distribution corresponding to green color region in the calibration curve.


Theory: uncertainty analysis estimates how great an effect the uncertainties in the individual measurements have on the calculated result.

Experimental uncertaintiesElectric currentVoltage of heaterLC readingsAir bulk temperatureHeat loss by conduction

Heat loss (conduction)

k: thermal conductivity of Plexiglas (= 0.2 W/m. K)A: area of heating surface (m2)L: Plexiglas thickness∆T: temperature difference across the heated surface (three K-typed thermocouples)

The estimated uncertainty of Nu was within ± 8%

Uncertainty analysis

LTAkQloss

Δ= ..

( )( ) AkTT

HQQNufbulkw

lossel

...

−−

=


Concluding remark

The consistency of the experimental data in the smooth duct by wide-band LCT gives confidence to pursue the effects of the confined jet with a shallow angle on convective heat transfer .


Next step

HT measurement in channel flow with single jet:U jet =35 m/s and Re = 100k

Heat foil

TLC

Measurement region

internal cooling of a hot turbine structure - lth · internal cooling of a hot turbine structure...

Documents