Transient Heat Transfer Measurements Using a Single Wide-Band Liquid Crystal Test

1999 ◽  
Vol 122 (3) ◽  
pp. 546-552 ◽  
Author(s):  
Dragos N. Licu ◽  
Matthew J. Findlay ◽  
Ian S. Gartshore ◽  
Martha Salcudean
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Film Cooling ◽  
Imaging System ◽  
Wide Band ◽  
Thermochromic Liquid Crystal ◽  
Film Cooling Effectiveness ◽  
Flame Ionization ◽  
Square Jets ◽  
True Color

A technique using a thermochromic liquid crystal coating to measure film cooling effectiveness (η) and heat transfer coefficient hf has been developed so that both of these important parameters can be obtained, as a function of time, from a single transient test. The technique combines a real-time, true color (24 bit) imaging system with the use of a wide-band liquid crystal coating and multiple event sampling for the simultaneous determination of η and hf from the single test. To illustrate and validate this technique, the flow from compound-angle square jets in a crossflow is examined. The tests, in which the jet air was suddenly heated to about 40°C, lasted 30 seconds. The measured η is compared with measurements made in the same flow under steady-state conditions in a totally different way, using a mass/heat analogy and a flame ionization detector. Good agreement is obtained. Three different blowing ratios M of 0.5, 1.0, and 1.5 are investigated with a constant jet Reynolds number of about 5000. Detailed quantitative comparisons of the η measured in both ways are made for all blowing ratios, and plots of η and hf are presented. [S0889-504X(00)01403-3]

scholarly journals Measurements of Heat Transfer Characteristics for Film Cooling Applications

1999 ◽  
Author(s):  
Dragos N. Licu ◽  
Matthew J. Findlay ◽  
Ian S. Gartshore ◽  
Martha Salcudean
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Imaging System ◽  
Wide Band ◽  
Test Case ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

A new experimental technique based on wide-band liquid crystal thermography and transient one-dimensional heat conduction has been developed and implemented. The technique combines a real-time, true colour imaging system with the use of a wide-band liquid crystal and multiple event sampling for the simultaneous determination of the film cooling effectiveness and heat transfer coefficient from one transient test. For a test case of compound angle square jets in a crossflow, very good agreement was obtained between the film cooling effectiveness calculated from the transient heat transfer experiments and the film cooling effectiveness measured in isothermal mass transfer experiments using a flame ionization detector technique. Three different blowing ratios of M = 0.5, 1.0, and 1.5 are investigated with a constant jet Reynolds number (Re2) of around 5000. Detailed quantitative comparisons of spanwise film cooling effectiveness profiles are made for all blowing ratios examined, and contour plots of film cooling effectiveness and heat transfer coefficient are also presented.

Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gages

2000 ◽  
Vol 122 (4) ◽  
pp. 709-716 ◽  
Author(s):  
S. M. Guo ◽  
C. C. Lai ◽  
T. V. Jones ◽  
M. L. G. Oldfield ◽  
G. D. Lock ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Transfer Coefficient ◽  
Rough Surface ◽  
Guide Vane ◽  
Wide Band ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled three-dimensional nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gages (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet free-stream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modeled to represent engine conditions by using a heavy “foreign gas” (30.2 percent SF6 and 69.8 percent Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented. The surfaces of interest are coated with wide-band thermochromic liquid crystals, which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of color is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed. Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in-service turbine blades and vanes, increases the heat transfer coefficient by up to 50 percent over the smooth surface level. The film cooling effectiveness is influenced less by the roughness. [S0889-504X(00)00804-7]

Measurement of Local Heat Transfer Coefficient and Film Cooling Effectiveness Through Discrete Holes

2000 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
C. H. N. Yuen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Density Ratio ◽  
Local Heat Transfer ◽  
Double Row ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

An efficient steady-state wide band liquid crystal technique is used to study the film cooling performance of a variety of geometries in a flat plate: a single row of holes, a double row of holes (both in-line and staggered), and a single cooling hole. This method allows temperature information to be captured in one image, without the difficulty involved in a transient experiment. The streamwise inclinations tested are 30°, 60°, and 90°. The freestream is maintained at 13m/s, and at ambient temperature. The range of blowing ratios varied from 0.33 to 2.0. Both heat transfer coefficient and adiabatic cooling effectiveness are measured for all the cases. Air is used to produce a density ratio near unity. From the range of blowing ratios tested, the most effective film cooling is achieved at a value close to 0.5, for near unity density ratio. It has been revealed that film cooling effectiveness is improved when the jet remains attached to the surface, however, this is generally coupled with an augmentation in heat transfer owing to the disturbance the attached jet causes to the boundary layer. The 30° inclined holes show to be the most effective. Results demonstrate the full coverage capability of liquid crystal thermography.

Comparison of Numerical Investigations With Measured Heat Transfer Performance of a Film Cooled Turbine Vane

2008 ◽  
Author(s):  
D. Charbonnier ◽  
P. Ott ◽  
M. Jonsson ◽  
Th. Ko¨bke ◽  
F. Cottier
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Measurement Data ◽  
External Flow ◽  
Test Model ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness

Detailed surface measurements of the heat transfer coefficient and the film cooling effectiveness by application of the transient liquid crystal method were carried out on a heavily film cooled nozzle guide vane (NGV) in a linear cascade wind tunnel at the EPFL as part of the European Research Project TATEF2 (Turbine Aero-Thermal External Flows 2). The external cooling setup included a showerhead cooling scheme and suction and pressure side of the airfoil several rows of fan-shaped cooling holes. By testing two different cooling flow rates at a NGV exit Reynolds number of 1.46E+06, detailed aerodynamic and heat transfer measurement data were obtained that can be used for validation of numerical codes and design tools for cooled airfoils. The data include the NGV surface static pressure distribution and wall heat transfer and film cooling effectiveness obtained by application of the transient liquid crystal technique. An engine representative density ratio between the coolant and the external hot gas flow was achieved by using CO2 as coolant gas. For the coupled simulation of internal cooling and external flow the numerical model was composed of the cooling air feeding the internal plenum, the cooling holes, and the outer external flow domain. An unstructured mesh was generated for the simulations by applying two different commercial CFD codes (Fluent and CFX). Identical boundary conditions were chosen in order to allow for a direct comparison of both codes. The computations were carried in two ways, first using a built-in transition model and second by imposing fully turbulent flow starting at the leading edge. For both codes the same built-in turbulence models were applied. The computations were set up to solve for the aerodynamic flow quantities both within and around the test model and for the thermal quantities on the vane surface, i.e. heat transfer coefficient and film cooling effectiveness. The computational results from the two codes are compared and validated against the results from the experiments. The numerical results were able to confirm a suspicion that the cross flow in the feeding plenum causes an observed non-symmetry of the measured film cooling effectiveness at the outlet of some cooling holes.

scholarly journals Experimental Study of Showerhead Cooling on a Cylinder Comparing Several Configurations Using Cylindrical and Shaped Holes

1999 ◽  
Vol 122 (1) ◽  
pp. 161-169 ◽  
Author(s):  
H. Reiss ◽  
A. Bo¨lcs
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Performance Enhancement ◽  
Turbine Blades ◽  
Density Ratio ◽  
Test Facility ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Shaped Hole

Film cooling and heat transfer measurements on a cylinder model have been conducted using the transient thermochromic liquid crystal technique. Three showerhead cooling configurations adapted to leading edge film cooling of gas turbine blades were directly compared: “classical” cylindrical holes versus two types of shaped hole exits. The experiments were carried out in a free jet test facility at two different flow conditions, Mach numbers M=0.14 and M=0.26, yielding Reynolds numbers based on the cylinder diameter of 8.6e4 and 1.55e5, respectively. All experiments were done at a mainstream turbulence level of Tu=7 percent with an integral length scale of Lx=9.1 mmM=0.14, or Lx=10.5 mmM=0.26, respectively. Foreign gas injection CO2 was used, yielding an engine-near density ratio of 1.6, with blowing ratios ranging from 0.6 to 1.5. Detailed experimental results are shown, including surface distributions of film cooling effectiveness and local heat transfer coefficients. Additionally, heat transfer and heat load augmentation due to injection with respect to the uncooled cylinder are reported. For a given cooling gas consumption, the laid-back shaped hole exits lead to a clear enhancement of the cooling performance compared to cylindrical exits, whereas laterally expanded holes give only slight performance enhancement. [S0889-504X(00)01801-8]

scholarly journals A Transient Method Using Liquid Crystal for Film Cooling Over a Convex surface

2001 ◽  
Vol 7 (3) ◽  
pp. 153-164 ◽  
Author(s):  
Ping-Hei Chen ◽  
Min-Sheng Hung ◽  
Pei-Pei Ding
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Convex Surface ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

In order to explore the effect of blowing ratio on film cooling over a convex surface, the present study adopts the transient liquid crystal thermography for the film cooling measurement on a straight circular hole configuration. The test piece has a strength of curvature(2r/D)of 92.5, pitch to diameter ratio(P/D)of 3 and streamwise injection angle(γ)of35∘All measurements were conducted under the mainstream Reynolds number(Red)of 1700 with turbulence intensity(Tu)of 3.8%, and the density ratio between coolant and mainstream(ρc/ρm)is 0.98. In current study, the effect of blowing ratio(M)on film cooling performance is investigated by varying the range of blowing ratio from 0.5 to 2.0. Two transient tests of different injection flow temperature were conducted to obtain both detailed heat transfer coefficient and film cooling effectiveness distributions of measured region. The present measured results show that both the spanwise averaged heat transfer coefficient and film cooling effectiveness increase with decreased blowing ratio.

scholarly journals Use of a Thermographic Phosphor Fluorescence Imaging System for Simultaneous Measurement of Film Cooling Effectiveness and Heat Transfer Coefficient

1996 ◽  
Author(s):  
M. K. Chyu ◽  
Y. C. Hsing
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Imaging System ◽  
Heating Process ◽  
Temperature Sensitive ◽  
Test Model ◽  
Film Cooling Effectiveness ◽  
Thermographic Phosphor

This paper describes a novel approach based on the temperature-sensitive fluorescence of a thermographic phosphor (europium-doped lanthanum oxysulfide, La2O2S:Eu+3) that enables the simultaneous determination of both local film effectiveness and local heat transfer on a film-cooled surface. The measurement system is capable of acquiring a series of transient, full-field surface temperature images during a heating process. Using a data reduction procedure designed specifically for three-temperature systems, these temporally resolved temperature maps yield the local film effectiveness and heat transfer coefficient simultaneously. The film cooling test model is a single row of four, 30-degree inclined, discrete holes oo a flat plate. The measuement results exhibit superior spatial resolution with detailed features in good agreement with those using other conventional thermal methods, as well as the liquid crystal imaging technique. One major advantage of this technique is its potential for high temperature and highly unsteady applications.

scholarly journals Utilization of the Transient Liquid Crystal Technique for Film Cooling Effectiveness and Heat Transfer Investigations on a Flat Plate and a Turbine Airfoil

1997 ◽  
Author(s):  
U. Drost ◽  
A. Bölcs ◽  
A. Hoffs
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Flat Plate ◽  
Film Cooling ◽  
Coolant Temperature ◽  
Double Row ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Single Row ◽  
Transient Liquid Crystal Technique

The transient liquid crystal technique has been used to measure film cooling effectiveness and heat transfer on a flat plate in a free jet, and a turbine airfoil in a linear cascade. A multiple-test regression method has been developed for the data reduction, considering a transient coolant temperature evolution. Flat plate film cooling was investigated for a single row of 35° inclined holes at Mach numbers of 0.3 and 0.5, and two turbulence intensities. Downstream of injection heat transfer was increased in-between the holes due to enhanced turbulence caused by the shearing of the coolant and the mainstream. At higher turbulence intensity the range of blowing ratios was broader as lift-off was delayed. Rim cooling measurements on the airfoil were conducted at engine-representative flow conditions. A maximum effectiveness of 0.3 behind injection was observed on the suction side, with slightly higher values for a double row in comparison to a single row configuration. Due to a high coolant momentum, the effectiveness on the pressure side was very low at about 0.05 for a single row configuration.

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