En byggnad bör uppfylla kraven gällande energianvändning och god inomhusmiljö. Byggnadens ventilationssystem arbetar med att upprätthålla god luftkvalitet samt effektiv energianvändning. Genom att styra och reglera luftflödet efter behov med ett Variable Air Volume system (VAV-system) kan ventilationssystemets energianvändning minska utan att göra avkall på luftkvalitén inomhus. VAV-apparater arbetar oftast vid ett lämpligt minimumflöde över tid, vilket medför att VAV- apparatens precision vid låga flöden är viktig. Studien har syfte till att undersöka noggrannheten i flödesmätningar vid låga luftflöden med tre VAV-apparater, som var och en representerar en särskild mätteknik samt med mätmetoderna anemometer och stos. Datainsamlingen genomfördes via mätningarna i laboratoriemiljö. Insamlade mätdata hanterades i kalkylbladsprogrammet Excel. De tre VAV-apparaterna som användes i studien var utrustade med mätmetoderna, tryckskillnad över VAV-spjäll, ultraljud samt tryckskillnad över korslagda pitotrör. För att undersöka VAV-apparaternas, varmtrådsanemometerns och luftflödesstosens mätresultat användes standardiserad strypflänsmätning som referens på grund av dess låga mätosäkerhet. Alla VAV-apparaterna undersöktes för samma börvärden, 4 l/s som lägst och 50 l/s som störst. Experimentet delades in i test 1 och 2. I test 1 jämfördes de olika mätmetoderna med strypflänsens mätresultat. I test 2 undersöktes VAV-apparaternas mätosäkerhet vid två olika inloppsförhållande, rak kanal och 90° böj. Resultatet av studiens tester visade att VAV-apparaternas största mätfel skedde vid de lägsta inställda börvärdena 4–6 l/s. Även de två andra mätmetoderna, flödesstos och varmtrådsanemometer, visade störst mätfel vid de lägsta börvärdena 5 och 10 l/s. För att undersöka hur noggrant VAV-apparaterna reglerade mot det inställda börvärdet jämfördes strypflänsens mätresultat med de inställda börvärdena. Resultatet visade i de flesta fall att dessa luftflöden ej stämde överens med varandra. Resultatet för skillnaden mellan VAV-apparaternas mätresultat när de utsattes för två olika inloppsförhållande visade ingen tydlig indikation på att inloppsförhållandet 90° böj var den förutsättning som gav det största mätfelet förutom för VAV-apparat med ultraljud. Mer erfarenhet av att utföra mätningar hade bidragit till bättre utförda mätningar. Om mätningen skulle utföras med dagens erfarenhet hade det utförts flera mätningar på samma börvärde för att se om mätresultaten varierade eller om det gick att se ett tydligt mönster i resultaten, vilket hade stärkt studiens slutresultat.

Wind resource assessment at California Polytechnic State University shows there is potential for wind power generation on Cal Poly land. A computational fluid dynamics model based on wind data collected from a campus maintained meteorological tower on Escuela Ranch approximately 5 miles northwest of campus suggests there are areas of Cal Poly land with an IEC Class III wind resource at a height of 80 meters above ground. In addition during the daytime when the campus uses the most energy there are large portions of land with annual average daytime wind speeds above 6.9m/s. These areas have been identified by analyzing the wind speed and directional data collected at the meteorological tower and using it to create the boundary conditions and turbulence parameters for the computer model. The model boundary conditions and turbulence parameters have been verified through comparison between data collected at Askervein hill in Scotland during the 1980’s and the results of a simulation of Askervein hill using the same model. Before constructing a wind farm for power generation, additional meteorological towers should be constructed in Poly Canyon to further confirm the wind resource prediction.

Two-Phase bubbly flows are encountered in a wide range of industrial applications, particularly where phase changes occur as seen in high performance heat exchangers and boiling reactors for power generation. These flows have been extensively studied in channels with circular geometries using air-water flows, though little data exists for flows through narrow rectangular channels. Measurements in thin geometries are particularly challenging since large bubbles bridge the gap, and it is difficult to compare point measurements with photographic techniques. The objective of this study is to explore the abilities of hot-film anemometry and high speed photography for taking measurements in a narrow vertical rectangular channel for a range of volume fractions, with particular attention on the narrow dimension. Hot-film anemometry (HFA) is a measurement technique originally developed for the measurement of fluid velocities, but has since been found to have applications for broader measurements in multiphase flow. With the sensor operating on the principle of heat loss, the method takes advantage of the differing abilities of the phases to transport heat, with each phase leaving its own signature in the signal response. The linchpin of this method lies in the ability to accurately distinguish between the two phases within the signal, and to execute this operation, various algorithms and techniques have been developed and used with some success for a wide range of flow conditions. This thesis is a study of the various methods of analysis such as amplitude threshold for triggering, and small slope threshold for finely tuning the edges of the bubble interactions, and demonstrates the capabilities of the hot-film sensor in a narrow rectangular vertical duct with a high aspect ratio. A vertical acrylic test section was fabricated for the purposes of this study, inset with a rectangular channel 38.1mm in width and 3.125mm in depth. Experiments were conducted for volume fractions ranging from 2% to 35%, which remained within the limits of the bubbly flow regime, but ranged from small uniform bubbles to larger bubbles coalescing into a transition regime. The hot-film signal was analyzed for void fraction, bubble speed, and bubble size. An in-depth study of the various methods of phase discrimination was performed and the effect of threshold selection was examined. High-speed video footage was taken in conjunction with the anemometer data for a detailed comparison between methods. The bubble speed was found to be in close agreement between the HFA and high-speed video, staying within 10% for volume fractions above 10%, but still remaining under a 30% difference for even as low as the 2% volume fraction, where measurements have been found to be historically difficult. The trends with volume fraction between the HFA and high-speed results were very similar. A correlation for narrow rectangular channels employing a simple drift flux model was found to compare with the void fraction data where appropriate. Good agreement was found between the methods using a hybrid phase discrimination technique for the HFA data for the void fraction and bubble speed results, with the high-speed video results showing a slight over-estimation in regards to the bubble size.

Technical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are currently underdeveloped for measuring these parameters in turbine engines. One of them is an optical-based non-contact technology. However, these nondirective measuring technologies lack the necessary accuracy, at least at present state. An alternative way to measure these parameters without disturbing the working environments is using MEMS type sensors. Currently, the techniques under development for such harsh environment applications are silicon carbide (SiC) and silicon nitrite (Si3N4) –based ceramic MEMS sensors. But those technologies present some limitation such as narrow processing method, high cost (materials and processing cost), and limited using temperatures (typically < 800 C). In this research we propose to develop two sensors based on recently developed polymer-derived ceramics (PDCs): Constant Temperature Hot wire Anemometer, temperature/heat-flux sensor for turbine applications. PDC is a new class of high temperature ceramics. As we shall describe below, many unique features of PDCs make them particularly suitable for the proposed sensors, including: excellent thermo-mechanical properties at high temperatures, enable high temperature operation of the devices; various well-developed processing technologies, such as injection molding,photolithography, embossing, DRIE etching and precise machining, can be used for the fabrication of the devices; and tunable electric conductivity, enable the proposed sensors fabricated from similar materials, thus reliability considerations associated with thermal mismatch, which is a big concern when using MEMS-based sensors at elevated temperatures, will be minimized.

A parametric study was performed to observe and quantify the effect of varying turbulence intensities on separation and performance in a compressor cascade at low Reynolds numbers. Tests were performed at 25° and 37.5° stagger angle, negative and positive angles of incidence up until the point of full stall, Reynolds numbers from 6 x 104 to 12.5 x 104, and turbulence intensities from approximately 0.7% – 8%. Additionally, oil flow techniques were combined with static tap data to visualize the boundary layer characteristics at various test conditions. The overall performance of the cascade was presented and evaluated through mass-averaged total pressure loss coefficients. The results of the study showed that the best efficiency (lowest pressure loss coefficient) was determined by separation characteristics for any angle of attack. While adding turbulence generally delayed separation, in some cases, adding turbulence to a separated airfoil resulted in decreased performance. Very similar separation characteristics were observed for the full range of Reynolds numbers and stagger, with the higher stagger setting giving slightly better performance. It was shown that a large percentage of total pressure losses can be recovered by applying the appropriate turbulence intensity at any angle of attack, which is relevant to possibilities for active control of such flows. / Master of Science

A three-component Laser Doppler Anemometer (LDA) instrument, an array of stationary thermocouples and a moving thermocouple were used to capture the three-dimensional flow and temperature fields for the system of two opposing axisymmetric turbulent jets. It was found that buoyancy-induced curvature of the hot jet resulted in cross shearing with the opposing jet. The following report will investigate the adequacy of the current experimental measurements for the identification of coherent structures and the characterization of their effects on the mean flow. Identification tools include the power spectra and conditional average velocity measurements based on the Window Average Gradient (WAG). It was determined that the low sampling and large spatial positions of the thermocouple measurements were not for the retrieval of quantitative turbulence data. For the velocity measurements, the LDA data were found to be adequate in regions of low turbulence intensities but degraded as the measurements approached the region where the two jet shear layers interacted. The detection of periodic structures from the power spectrum was inconclusive due to noise. The WAG algorithm was affected by the irregular sampling and required modification. For the events detected, an intermittency factor of 16.4% at the interaction region of two shear layers was observed. In addition, these results suggest that these events contribute 30% of the mean momentum transfer across the jet. Furthermore, the contribution of these events to the lateral component of the turbulent kinetic energy was nearly eight times larger than the contributions to the axial or transverse direction. / Thesis / Master of Engineering (ME)

No description available.

A building must meet requirements related to energy usage and good indoor environment. The building ́s ventilation system aims to maintain optimal air quality, thermal condition, and efficient energy usage. By being able to control and adjust airflow as needed with a Variable Air Volume (VAV) system, energy usage of the ventilation system can be reduced without sacrificing indoor air quality. The VAV system operates with a variable airflow, so the accuracy of the VAV terminal at low flows is important. The study aims to verify the accuracy of three different methods for measuring airflow: iris damper, hot- wire anemometer, and volume flow hood. Data collection was carried out through measurements in a laboratory environment. The collected data were managed in the Excel spreadsheet program. The three methods were tested on a prototype consisting of a supply airline and an exhaust airline, each equipped with a VAV unit that varied the airflow through a potentiometer, allowing different airflow values to be obtained for the experiment. The results of the iris damper method were chosen as reference for the other methods due to its ability to predict results using manufacturer tables, which provide useful information about airflow values when varying pressure drop and the iris damper loss k-factor. In this way, set points were stablished for all tests. Two experiments were conducted with different set points. In retrospect it is acknowledged that an air flow meter of higher accuracy had been needed to ascertain the results of the study. That said, the attained results indicate the following: In the experiments, measurements were taken for 12 different airflow values, ranging from 200 l/s to 20 l/s. The test results showed that the most inaccurate method was the volume flow hood, with an average error ranging from ±19% to ±49%, followed by the hot wire anemometer, which had a measurement error between ±15% to ±18%. The high inaccuracy of the volume flow hood was due to a lack of instrument recalibration, resulting in highly inaccurate measurements. All methods showed lower uncertainty between 20 l/s and 50 l/s. Finally, it was verified that the iris damper method improved its average reading error by increasing the pressure drop across the damper and reducing its loss k-factor, achieving the lowest error of the entire experiment at ±12%.

Non-intrusive acoustic instruments that measure fluid velocity and temperature have been restricted to low subsonic Mach number applications due to increased complexities associated with acoustic refraction, low signal-to-noise ratios, and a limited range of practical applications. In the current work, the use of acoustics for non-intrusive flow monitoring in compressible flows is explored and a novel sonic anemometry and thermometry (SAT) technique is developed. Using multiple arrangements of SAT equipment, a compressible acoustic tomography technique was also developed to resolve flow non-uniformities. Three validation experiments were used to investigate the novel SAT technique performance, and a fourth validation experiment was used to explore compressible flow tomography capabilities. In the first experiment, an unheated jet was used to verify that the acoustic technique could measure fluid velocities in high subsonic Mach number flows. The application demonstrated velocity root mean square (RMS) errors of 9 m/s in unheated jet flows up to Mach 0.83. Next, a heated jet facility was used to assess the impact of fluid temperature on measurement accuracy. Using jet Mach numbers up to 0.7 and total temperatures up to 700 K, RMS velocity and static temperature errors up to 8.5 m/s (2.4% of maximum jet velocity) and 23.3 K (3.3% of total temperature) were observed. Finally, the acoustic technique was implemented at the exhaust of a JT15D-1A turbofan engine to investigate technique sensitivity to bypass engine conditions. A mass flow rate and thrust estimation approach was developed and RMS errors of 1.1 kg/s and 200 N were observed in conditions up to an exhaust Mach number of 0.48. Since modern acoustic tomography techniques require an incompressible flow assumption for velocity detection, advancements were made to extend acoustic tomography methods to compressible flow scenarios for the final experiment. The approach was tested in the heated jet operating at Mach 0.48 and 0.72 (total temperature of 675 K, approximately 2.25 times the ambient) and numerical simulations were used to identify technique sensitivity to input variables and system design. This research marks the first time an acoustic method has been used to estimate compressible flow velocities and temperatures. / Ph. D.

The effects of grid generated free-stream turbulence on compressor cascade performance was measured experimentally in the Virginia Tech blow-down wind tunnel. The parameter of key interest was the behavior of the measured total pressure loss coefficient with and without generated free-stream turbulence. A staggered cascade of nine airfoils was tested at a range of Mach numbers between 0.59 and 0.88. The airfoils were tested at both the lowest loss level cascade angle and extreme positive and negative cascade angles about this condition. The cascade was tested in a Reynolds number range based on the chord length of approximately 1.2-2x106. A passive turbulent grid was used as the turbulence-generating device, it produced a turbulent intensity of approximately 1.6%. The total pressure loss coefficient was reduced by 11-56% at both the "lowest loss level" and more positive cascade angles for both high and low Mach numbers. Oil Visualization and blade static pressure measurements were performed in order to gain a qualitative understanding of the loss reduction mechanism. The results indicate that the effectiveness of an increasing turbulent free-stream on loss reduction, at transonic Mach numbers, depends on whether the shock wave on the suction surface is strong enough to completely separate the boundary layer. At negative cascade angles, increasing free-stream turbulence proved to have a negligible influence on the pressure loss coefficient. At cascade angles where transition exists within a laminar separation bubble, increasing free-stream turbulence suppressed the extent of the laminar separation bubble and led to an earlier turbulent reattachment. / Master of Science