Zachary Little

A Detailed Uncertainty Analysis of Adiabatic Film Cooling Effectiveness Measurements Using Pressure Sensitive Paint

Pressure sensitive paint (PSP) can be a powerful tool in measuring the adiabatic film cooling effectiveness. There are two distinct sources of error for this measurement technique; the ability to experimentally obtain the data and the validity of the heat and mass transfer analogy for the problem being studied. This paper will assess the experimental aspect of this PSP measurement specifically for film cooling applications.Experiments are conducted in an effort to quantifiably bound expected errors associated with temperature non-uniformities in testing and photo-degradation effects. Results show that if careful experimental procedures are put in place, both of these effects can be maintained to have less than 0.022 impact on effectiveness.Through accurate semi-in-situ calibration down to 4% atmospheric pressure, the near-hole distribution of effectiveness is measured with high accuracy. PSP calibrations are performed for multiple coupons, over multiple days. In addition, to reach a partial pressure of 0 the calibration vessel was purged of all air by flowing CO2.The primary contribution of this paper lies in the uncertainty analysis performed on the PSP measurement technique. A thorough uncertainty analysis is conducted and described, in order to completely understand the presented measurements and any shortcomings of the PSP technique. This quantification results in larger, albeit more realistic, values of uncertainty, and helps provide a better understanding of film cooling effectiveness measurements taken using the PSP technique. The presented uncertainty analysis takes into account all random error sources associated with sampling and calibration, from intensities to effectiveness.Adiabatic film cooling effectiveness measurements are obtained for a single row of film cooling holes inclined at 20 degrees, with CO2 used as coolant. Data is obtained for six blowing ratios. Maps of uncertainty corresponding to each effectiveness profile are available for each test case. These maps show that the uncertainty varies spatially over the test surface, high effectiveness corresponds to low uncertainty. The noise floors can be as high as 0.04 at effectiveness levels of 0. Day-to-day repeatability is presented for each blowing ratio and shows that laterally averaged effectiveness data is repeatable within 0.02 effectiveness.Copyright

A Detailed Uncertainty Analysis of Adiabatic Film Cooling Effectiveness Measurements Using Pressure-Sensitive Paint

Pressure-sensitive paint (PSP) can be a powerful tool in measuring the adiabatic film cooling effectiveness. There are two distinct sources of error for this measurement technique: the ability to experimentally obtain the data and the validity of the heat and mass transfer analogy for the problem being studied. This paper will assess the experimental aspect of this PSP measurement specifically for film cooling applications. Experiments are conducted in an effort to quantifiably bound expected errors associated with temperature nonuniformities in testing and photodegradation effects. Results show that if careful experimental procedures are put in place, both of these effects can be maintained to have less than 0.022 impact on effectiveness. Through accurate semi in situ calibration down to 4% atmospheric pressure, the near-hole distribution of effectiveness is measured with high accuracy. PSP calibrations are performed for multiple coupons, over multiple days. In addition, to reach a partial pressure of zero the calibration vessel was purged of all air by flowing CO2. The primary contribution of this paper lies in the uncertainty analysis performed on the PSP measurement technique. A thorough uncertainty analysis is conducted and described, in order to completely understand the presented measurements and any shortcomings of the PSP technique. This quantification results in larger, albeit more realistic, values of uncertainty and helps provide a better understanding of film cooling effectiveness measurements taken using the PSP technique. The presented uncertainty analysis takes into account all random error sources associated with sampling and calibration, from intensities to effectiveness. Adiabatic film cooling effectiveness measurements are obtained for a single row of film cooling holes inclined at 20 deg, with CO2 used as coolant. Data are obtained for six blowing ratios. Maps of uncertainty corresponding to each effectiveness profile are available for each test case. These maps show that the uncertainty varies spatially over the test surface and high effectiveness corresponds to low uncertainty. The noise floors can be as high as 0.04 at effectiveness levels of 0. Day-to-day repeatability is presented for each blowing ratio and shows that laterally averaged effectiveness data are repeatable within 0.02 effectiveness.

Heat Transfer Measurements Using the Hybrid Heat Transfer Technique With Thermally Adiabatic and Participating Ribs

This work is focused on the application of a number of improvements to the traditional transient thermochromic liquid crystals technique, in particular the hybrid heat transfer experiment, in order to provide more detailed and accurate measurements of the surface heat transfer coefficient in internal cooling passages. More accurate measurements of heat transfer coefficient are necessary to provide a clearer understanding of the performance of the cooling channels and to not misrepresent the channel performance so that more optimal designs and progress can be achieved. Detailed Nusselt number measurements were performed for a square channel with ribs on one wall in the Reynolds number range of 50 000 to 150 000, based on channel hydraulic diameter, using the transient thermochromic liquid crystals technique. The rib aspect ratio is 1:1, the rib height-to-hydraulic diameter ratio is 0.10, the rib-pitch–to–rib-height ratio is 10, and the ribs are oriented orthogonal to the streamwise direction. Heat transfer measurements were taken on all four walls so that the bulk temperature variation throughout the channel during the experiment can also be taken into account. Adiabatic and aluminum ribs were used simultaneously. The recently developed Coupled 0D-1D model is used to resolve the average heat transfer of the metallic rib features. A comparison of the data obtained using adiabatic and metallic rib features is made to quantify experimentally the influence of the rib-induced contamination. Friction augmentation, overall heat transfer augmentation, and overall thermal performance are also reported.Copyright

Adiabatic Film Cooling Effectiveness Measurements Throughout Multi-Row Film Cooling Arrays

Adiabatic film cooling effectiveness measurements are obtained using pressure-sensitive paint (PSP) on a flat film cooled surface. The effects of blowing ratio and hole spacing are investigated for four multi-row arrays comprised of 8 rows containing 52 holes of 3.8 mm diameter with 20° inclination angles and hole length-to-diameter ratio of 11.2.The four arrays investigated have two different hole-to-hole spacings composed of cylindrical and diffuser holes. For the first case, lateral and streamwise pitches are 7.5 times the diameter. For the second case, pitch-to-diameter ratio is 14 in lateral direction and 10 in the streamwise direction. The holes are in a staggered arrangement. Adiabatic effectiveness measurements are taken for a blowing ratio range of 0.3 to 1.2 and a density ratio of 1.5, with CO2 injected as the coolant.A thorough boundary layer analysis is presented, and data was taken using hotwire anemometry with air injection, with boundary layer and turbulence measurements taken at multiple locations in order to characterize the boundary layer. Local effectiveness, laterally averaged effectiveness, boundary layer thickness, momentum thickness, turbulence intensity and turbulence length scale are presented. For the cylindrical holes, at the first row of injection, the film jets are still attached at a blowing ratio of 0.3. By a blowing ratio of 0.5, the jet is observed to lift off, and then impinge back onto the test surface. At a blowing ratio of 1.2, the jets lift off, but reattach much further downstream, spreading the coolant further along the test surface. A thorough uncertainty analysis has been conducted in order to fully understand the presented measurements and any shortcomings of the measurement technique. The maximum uncertainty of effectiveness and blowing ratio is 0.02 counts of effectiveness and 3 percent respectively.Copyright

Numerical Simulations of a Rectangular Channel with Symmetric and Non-symmetric Wedge-shaped Turbulators

This work is an investigation of the flow field in a narrow rectangular duct with wedge turbulators applied. The Reynolds numbers studied are 10 000, 20 000, 30 000, and 40 000. Two different wedge-shaped transport promoters are studied, a symmetric and a nonsymmetric wedges. Only channel configurations with wedges applied to the two opposite wide walls are included in the study. The flow fields in these channels are obtained numerically using RANS-based CFD approach. The purpose of the flow field investigation is to provide a better understanding of the mechanism of heat transport and explain the better thermal performance of channels with wedge-shaped turbulators compared to rib turbulators. Data reported includes numerical predictions of the heat transfer and friction performance of the wedge channels. Vortex trajectories are identified using the Q-criterion and Λ2.

The Effect of Inclination Angle on Turbulent Quantities of a Single Row of Cylindrical Jets in Crossflow

This is an experimental investigation into the effect of inclination angle and lateral spacing on the variation of mean/turbulent velocity profiles for a single row of cylindrical jets issuing into a turbulent boundary layer. Extensive velocity measurements are made in the region near injection for a single row of film cooling holes, to determine how hole orientation affects turbulent length scales and aerodynamic performance. Inclination angles of 30°, 35°, 45°, 60°, 75°, and 90° are tested, while the film cooling hole’s length (L/D) and lateral spacing’s (P/D) are fixed for each angle at 4.25 and 3, respectively. The measurement domain exists from x/D=0 to 3, y/D=-1.5 to 1.5 and z/D=0 to 2 at nominal blowing ratios of M=0.5, 1, and 1.5. This data represents an extension of the flow measurements previously available in literature, and supplements companion heat transfer studies performed with the same experimental setup and test specimen. Experimental measurements of turbulence will be expressed by mean and fluctuating velocity, length and time-scales, spectral analysis, and flat plate boundary layer thickness calculations. Such turbulence quantification for a single row of cylindrical holes at various inclination angles will provide assistance for better formulation of boundary conditions and turbulence specification in Computational Fluid Dynamics (CFD) simulations.

Characterization of Thermochromic Liquid Crystals for Multi-Color Transient Heat Transfer Experiments

This study focuses on the calibration of non-encapsulated spray-able thermochromic liquid crystals (TLC). The TLC is calibrated on a copper block with thermistors and is recorded with cameras at 0°, 15°, 30°, and 45°. The influence of viewing angle on the perceived peak temperature is investigated as well as the long-term stability of TLC characteristics. Typical transient heat transfer experimenters utilize only the green peak temperature. In this work, it is demonstrated that the calibration of TLC yielding two distinct color peaks (for the red and green signal) are feasible and can be accurately obtained. The multi-color technique is an improvement of the traditional single-color technique used in transient heat transfer experiments. This multi-color technique enables two independent measurements of the surface temperature and will double the yield of usable data in future transient heat transfer experiments. The technique can be further expanded to incorporate multiple TLC mixtures and multi-band multi-color techniques can also be employed.

A Multi-Color Thermochromic Liquid Crystals Technique for Transient Heat Transfer Experiments

This paper demonstrates a technique to obtain multiple independent measurements of surface temperature using a single band thermochromic liquid crystals mixture for improved accuracy over single surface measurement techniques. Detailed Nusselt number measurements were performed for a square, smooth-walled channel in the Reynolds number range of 50 000 to 150 000, based on channel hydraulic diameter, using the transient thermochromic liquid crystals technique. Heat transfer measurements were taken on all four walls so that the bulk temperature variation throughout the channel during the experiment can also be taken into account. Data are post processed using the traditional single color technique and compared to the new multicolor technique. The proposed multicolor technique can complement existing single color, multiband techniques without added complexity.