The effects of using an insert Heat Flux Microsensor (HFM) versus an HFM deposited directly on a turbine blade to measure heat flux in a transonic cascade are investigated. The HFM is a thin-film sensor, 6.35 mm (0.250") in diameter (for an insert gage, including the housing) which measures heat flux and surface temperature. The thermal time response of both gages was modeled using a 1-D, finite difference technique and a 2-D, finite element solver. The transient response of the directly deposited gage was also tested against insert gages using an unsteady shock wave in a bench test setup and using a laser of known output. The effects of physical gage offset from the blade surface were also investigated. The physical offset of an insert HFM near the stagnation point on the suction side of a turbine blade was intentionally varied and the average heat transfer coefficient measured. Turbulence grids were used to study how offset affects the heat transfer coefficient with freestream turbulence added to the flow. The time constant of the directly deposited gage was measured to be 856 ms compared to less than 30 ms for the insert gages. Model results predict less than 20 ms for both gages and rule out the anodization layer (used for electrical isolation of the directly deposited gage from the blade) as the cause for the directly deposited gage's much slower time response. Offsets of ± 0.254 mm (0.010") at the gage location with an estimated boundary layer thickness of 0.10 mm (0.004") produced a higher average heat transfer coefficient than the 0.000" offset case. Using an insert HFM resulted in a higher average heat transfer coefficient than using the directly deposited gage and reduced the effects of freestream turbulence. To accurately measure heat transfer coefficients and the effects of freestream turbulence, the disruption of the flow caused by a gage must be minimized. Depositing a gage directly on the blade minimizes the effects of offset, but the cause of the slow time response must first be resolved if high speed data is to be taken. / Master of Science

The effects of grid generated freestream turbulence on surface heat transfer to turbine blades were measured experimentally. Time-resolved and unsteady heat flux measurements were made with Heat Flux Microsensors at two positions on the suction side of turbine blades. The experiments were conducted on a stationary cascade of aluminum turbine blades for heated runs at transonic conditions. Non-dimensional flow parameters were matched to actual engine conditions including the design exit Mach number of 1.26 and the gas-to-wall temperature ratio of 1.4. Methods for determining the adiabatic wall temperature and heat transfer coefficient are presented and the results are compared to computer predictions for these blades. Heat transfer measurements were taken with a new, directly deposited HFM gage near the trailing edge shock on nitrogen cooled blades. The average heat transfer coefficient for Mach 1.26 was 765 W/(m² °C) and matched well with a predicted value of 738 W/(m² °C). Freestream turbulence effects were studied at a second gage location 1.0 cm from the stagnation point on uncooled blades. Results at this location show an increase in freestream turbulence from 1 % to 8% led to a 15% increase of the average heat transfer coefficient and also matched well with predictions. The fast response time of the HFM illustrated graphically the increase in energy spectra due to freestream turbulence at the 0 - 10kHz range. The heat flux turbulence intensity (Tu_q) was defined as another physical quantity important to turbine blade heat transfer. / Master of Science

The Meyers et al. (2007) Tampa Bay Model produces water level and three-dimensional current and salinity fields for Tampa Bay. It is capable of computing temperature but is presently run without active thermodynamics. Variations in water temperature are driven by heat exchange at the water-atmosphere boundary and advective heat flux at the mouth of the bay. The net heat exchange surface boundary condition is required for computations of three-dimensional temperature fields. Components of the surface heat budget were measured or derived at an observational tower in Middle Tampa Bay. Net heat exchange at the surface of Tampa Bay was computed from June 2002 to May 2005. Total heat energy gained or lost at the bay-atmosphere interface includes turbulent and radiative heat fluxes. An initial examination of turbulent heat exchange, the portion of total surface heat flux driven by atmospheric turbulence, demonstrated the skill of a bulk flux algorithm (TOGA COARE v. 3.0) in predicting measured sensible heat flux over Tampa Bay (R² = 0.80 and RMSE of 11.02 W/m² from June through November of 2002). Insolation was measured directly at the observational tower. Solar radiation is reflected in proportion to sea surface albedo, computed following Payne (1972). Based upon Secchi depth readings, Tampa Bay was classified as a water body type 7. The amount of penetrating insolation reflected from the bottom was computed for this type 7 estuary. Upwelling longwave radiation is emitted in proportion to the water temperature according to the Stefan-Boltzmann law. Eleven bulk formulas for computing downwelling longwave radiation were assessed for skill in reproducing observations made at buoys moored on the West Florida Shelf. Berliand and Berliand (1952) best represented downwelling longwave heat flux measurements at the buoys and is appropriate for application over Tampa Bay. Surface heat flux dominates cooling in fall and warming in spring while advective heat exchange becomes important during the summer. Extreme events, including tropical cyclones and extratropical fronts, dramatically impact surface heat exchange, driving rapid cooling. The methods applied in computation of heat flux components are amenable to real-time modeling exercises.

No description available.

The purpose of this study is to quantify the effects of heat flux sensor design and interaction with both test article material choice and geometry on heat flux measurements. It is the public domain component of a larger study documenting issues inherent in heat flux measurement. Direct and indirect heat flux measurement techniques were tested in three thermally diverse model materials at the same Mach 6 test condition, with a total pressure of 1200 psi and total temperature of 1188° R, and compared to the steady analytic Fay-Riddell solution for the stagnation heat flux on a hemisphere. A 1/8 in. fast response Schmidt-Boelter gage and a 1/16 in. Coaxial thermocouple mounted in ¾ in. diameter stainless steel, MACOR, and Graphite hemispheres were chosen as the test articles for this study. An inverse heat flux calculation was performed using the coaxial thermocouple temperature data for comparison with the Schmidt-Boelter gage. Before wind tunnel testing, the model/sensor combinations were tested in a radiative heat flux calibration rig at known static and dynamic heat fluxes from 1 to 20 BTU/ft2/s. During wind tunnel testing, the chosen conditions yielded stagnation point convective heat flux of 15-60 BTU/ft2/s, depending on the stagnation point wall temperature of the model. A computational fluid dynamic study with conjugate heat transfer was also undertaken to further study the complex mechanisms at work. The overall study yielded complex results that prove classic methodology for inverse heat flux calculation and direct heat flux measurement require more knowledge of the thermal environment than a simple match of material properties. Internal and external model geometry, spatial and temporal variations of the heat flux, and the level of thermal contact between the sensor and the test article can all result in a calculated or measured heat flux that is not correct even with a thermally matched sensor. The results of this study supported the conclusions of many previous studies but also examined the complex physics involved across heat flux measurement techniques using new tools, and some general guidance for heat flux sensor design and use, and suggestions for further research are provided. / Ph. D.

published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

No description available.

Numerical experiments assuming land-use distributions of different heterogeneity of wet and dry surfaces were performed on a cloudy day in spring with a calm wind to examine their influences on the domain-averaged fluxes as well as on the distribution of the fluxes within the domain. The results substantiate that, for ]arge heterogeneity, i.e., small patches, the distribution of the patches plays no role in the magnitude of the atmospheric fluxes. For !arger patches, however, the domain-averaged latent heat-fluxes depend appreciably on both the heterogeneity as well as on the fractional coverage by the land-use types. On the average, for heterogeneous conditions, the prevailing land-use type governs the fluxes. Nevertheless, no exact linearity between the fractionally coverage of the two land-use types and the resulting fluxes exists. Discontinuities in the fluxes which lead to the non-linear behaviour of the domain-averaged fluxes occur at the border between two !arger areas of extremely different characteristics, namely, grass (wet, cool) and sand (dry, warm). Three different patterns of behaviour are found for the temporal development of the differences in the domain-averaged fluxes which depend on both the heterogeneity and the pattern of the land use. / Numerische Experimente, bei denen unterschiedlich heterogene Landnutzungsverteilungen trockener und feuchte Flächen angenommen werden, wurden für einen wolkigen Schwachwindtag im Frühjahr durchgeführt. Die Ergebnisse belegen, daß bei großer Heterogenität, d.h. kleinen Flächen, deren Anordnung keine Rolle spielt. Bei großen Flächen jedoch hängen die Gebietsmittelwerte der latenten Wärmeflüsse merklich sowohl von der Heterogenität als auch von dem Flächenanteil der Landnutzung ab. Im Mittel beherrscht der vorherrschende Landnutzungstyp die Flüsse. Dennoch ist kein exaktes lineares Verhalten zwischen dem Flächenanteil der Landnutzung und den resultierenden Flüssen vorhanden. Diskontinuitäten in der Verteilung der Flüsse, die letztendlich zu der Nichtlinearität der Gebietsmittelwerte der Flüsse führen, treten an den Grenzen der größeren Flächen unterschiedlicher Oberflächencharakteristika auf, in dieser Studie Gras (feucht, kühl) und Sand (trocken, warm). Drei unterschiedliche Verhaltensweisen im zeitlichen Verlauf der Differenzen der Gebietsmittelwerte der Flüsse wurden gefunden, die vom Muster und der Heterogenität der Landnutzung abhängen.

De Bruin och Hartogensis har föreslagit en ny metod för att beräkna impulsflödet och det sensibla värmeflödet vid stabila förhållanden. Metoden bygger på att de normaliserade standardavvikelserna är approximativt konstanta för den horisontella vinden och temperaturen. Beräkningarna görs endast utifrån medelvinden och temperaturen och dess standardavvikelser. Den här metoden testas i den här studien med datamaterial från Labans kvarnar på Gotland i Östersjön och Östergarnsholm som ligger 4 km utanför Gotland. Labans kvarnar representerar flöden över land och Östergarnsholm flöden över hav. Konstanterna som De Bruin och Hartogensis använde är följande: Cu=2.5 och CT=2.3, vilket gav en mycket liten spridning i deras beräkningar av flöden. Datamaterialet de använde sig av var från Kansas, USA, över en plan grässlätt. Olika statistiska mått har här testats för att erhålla värden på konstanterna. Medel-, median- och typvärde för de normaliserade standardavvikelserna för respektive kvantitet har beräknats. För landförhållanden i den här studien fås lite högre värden på konstanterna, Cu=2.6 och CT=2.6, än vad De Bruin och Hartogensis erhöll.  Vid beräkningar av flöden över hav delas vindriktningen upp i två intervall. Vindriktningen som ligger mellan 220o - 300o representerar vindar som blåser ifrån Gotland och vindriktningar som ligger mellan 80o - 220o representerar vindar från öppet hav. För öppna havsförhållanden fås konstanter som har ett lägre värde vid beräkning av impulsflödet, Cu=2.2 , än de värde som De Bruin och Hartogensis fick. För vindar som blåser ifrån Gotland erhålls konstanten till:Cu=3.0. Konstanter för beräkning av värmeflödet är svårare att bestämma och ger inte alls lika bra resultat över hav som för impulsflödet. Bestämningar av värmeflöde är mycket mer komplicerade än för impulsflöde. Delvis på grund av att det behövs två konstanter, men det beror också på att temperaturstrukturen i det marina gränsskiktet inte följer Monin-Obukhovs similaritetsteori.Framsidans foto / De Bruin and Hartogensis have proposed a new method to determine momentum flux and sensible heat flux at stable conditions. When using this method the assumption is made that the standard deviations for the longitudinal wind component and temperature are approximately constant. Only the mean wind and the temperature and the standard deviations are necessary for the calculations. The method has been analyzed in this study with data from Labans kvarnar sited on Gotland in the Baltic Sea and Östergarnsholm which is situated 4 km outside Gotland. Labans kvarnar represents fluxes over land and Östergarnsholm represents fluxes over sea. The constants that De Bruin and Hartogensis found are the following:Cu=2.5 for wind speed and CT=2.3  for temperature, which shows very little scatter in the calculations of the fluxes. The data they used where measured in Kansas over a very flat grassland site. Different statistics measurements have been tested to receive values of the constants. In search of constants the mean value, median value and the modal value for respectively quantity have been calculated. For land conditions the values of the constants are a little bit higher, Cu=2.6 and CT=2.6, than the values De Bruin and Hartogensis received. When calculating the fluxes over ocean the wind direction is divided in to two intervals. The wind direction between 220o - 300o represents winds from Gotland and wind direction between  80o - 220o represents winds from open sea. For the open sea conditions the constants calculated for the momentum flux in this study are a little bit lower, Cu=2.2, than the value De Bruin and Hartogensis found. For winds from Gotland the constant for momentum flux was found to be: Cu=3.0. When calculating the sensible heat flux the constants are very difficult to find and do not give as good result as for the momentum flux over sea. The conditions for the sensible heat are much more complicated than it is for momentum flux. Firstly two constants are needed and secondly the temperature structure in the marine boundary layer does not follow Monin-Obukhov similarity theory.

Die Surface Renewal Analysis wurde zur Bestimmung sensibler Wärmeflußdichten im bodennahen Bereich der atmosphärischen Grenzschicht genutzt und mit der Eddy - Korrelations - Methode verglichen. Dazu wurden beide Berechnungsmethoden auf Temperatur - und Vertikalwinddaten angewandt, die unter Verwendung von Strukturfunktionen simuliert wurden. Zur Überprüfung der Resultate wurden über zwei verschiedenen Unterlagen (Wiese und Düne) hochfrequente Zeitreihen von Temperatur und Vertikalwind gemessen und mit der Surface Renewal Analysis und der Eddy - Korrelations - Methode analysiert. / The Surface Renewal Analysis was used to estimate the sensible heat flux density in the ground near area of the boundary layer. The results were compared with eddy correlation method. For it both methods were used to analyse temperature- and vertical velocity-data, which were simulated by the application of structure functions. Time series of high frequency temperature- and vertical velocity-data over two different canopies (meadow and dune) were measured to examine the results. The data were analysed with surface renewal analysis and eddy correlation.