Previous studies have demonstrated that EPA approved federal reference method (FRM) samplers can substantially misrepresent the fractions of particles being emitted from agricultural operations due to the relationship between the performance characteristics of these samplers and existing ambient conditions. Controlled testing in a wind tunnel is needed to obtain a clearer understanding and quantification of the performance shifts of these samplers under varying aerosol concentrations, wind speeds and dust types. In this study, sampler performance was tested in a controlled environment wind tunnel meeting EPA requirements for particulate matter (PM) sampler evaluation. The samplers evaluated included two low-volume PM10 and Total Suspended Particulate (TSP) pre-separators. The masses and particle size distributions (PSDs) obtained from the filters of tested samplers were compared to those of a collocated isokinetic sampler. Sampler performance was documented using two parameters: cut-point (d_50) and slope. The cut-point is the particle diameter corresponding to 50% collection efficiency of the pre-separator while the slope is the ratio of particle sizes corresponding to cumulative collection efficiencies of 84.1% and 50% (d_84.1/d_50) or 50% and 15.9% (d_50/d_15.9) or the square root of 84.1% and 15.9% (d_84.1/d_ 15.9). The test variables included three levels of wind speeds (2-, 8-, and 24-km/h), five aerosol concentrations varying from 150 to 1,500 mu g/m3 and three aerosols with different PSDs (ultrafine Arizona Road Dust (ARD), fine ARD and cornstarch). No differences were detected between the performance of the flat and louvered FRM PM10 samplers (a = 0.05). The mean cut-point of both the PM10 samplers was 12.23 mu m while the mean slope was 2.46. The mean cut-point and slope values were statistically different from the upper limit of EPA-specified performance criteria of 10.5 mu m for the cut-point and 1.6 for the slope. The PM10 samplers over-sampled cornstarch but under-sampled ultrafine and fine ARD. The performance of the dome-top TSP sampler was close to the isokinetic sampler, and thus it can be used as a reference sampler in field sampling campaigns to determine true PM concentrations. There were large variations in the performance of the cone-top TSP samplers as compared to the isokinetic sampler. Dust type and wind speed along with their interaction had an impact on sampler performance. Cut-points of PM10 samplers were found to increase with increasing wind speeds. Aerosol concentration did not impact the cut-points and slopes of the tested samplers even though their interaction with dust types and wind speeds had an impact on sampler performance.

Low disturbance wind tunnels, such as the Klebanoff–Saric Wind Tunnel (KSWT), offer an ideal environment to study boundary layer transition. In particular, the leading-edge receptivity of sound can be measured by creating acoustic disturbances that interact with the leading edge of a model to create Tollmien–Schlichting Waves. The magnitude and composition (sound, turbulence) of the background disturbances can affect these experiments, so the background disturbances should be minimized and documented thoroughly. The purpose of this thesis is to document the background acoustic signature of the KSWT and describe infrastructure upgrades for acoustic receptivity experiments. The measurements presented in this thesis will support future receptivity measurements in the KSWT. Microphone measurements revealed several important acoustic features in the tunnel. Cross correlations showed that two sources of low-frequency unsteadiness (the extended diffuser and corner two) create large pressure fluctuations that dominate the pressure spectrum. Directional separation of waves in the test section revealed that motor and blade passing noise travels primarily upstream into the test section. Finally, the acoustic treatments in the plenum are effective at removing sound from the tunnel. A wall of speakers was installed in the plenum to enable acoustic receptivity experiments. The speakers create both the primary downstream traveling waves and reflected upstream traveling waves in the test section. An adaptive closed loop control system was installed to reduce the amplitude of the reflected waves during acoustic forcing. Although the performance of the control system is frequency dependent, the technique was implemented successfully. The reduction in the diffuser reflection will increase the quality of future acoustic receptivity experiments in the KSWT.

<p>This thesis deals with the problems of scaling aerodynamic data from wind tunnel conditions to free flight. The main challenges when this scaling should be performed is how the model support, wall interference and the potentially lower Reynolds number in the wind tunnel should be corrected.</p><p>Computational Fluid Dynamics (CFD) simulations have been performed on a modern transonic transport aircraft in order to reveal Reynolds number effects and how these should be scaled accurately. This investigation also examined how the European Transonic Wind tunnel (ETW) twin sting model support influences the flow over the aircraft. In order to further examine Reynolds number effects a MATLAB based code capable of extracting local boundary layer properties from structured and unstructured CFD calculations have been developed and validated against wind tunnel measurements. A general scaling methodology is presented.</p>

Thesis (M. Sc.)--University of Hong Kong, 1982.

Designing wind driven cross ventilation for a building is challenging due to the dynamic characteristics of wind. While numerous studies have studied various aspects of cross ventilation, few have had an opportunity to examine the topic with a holistic approach utilizing multiple research techniques. Thus, this dissertation combined three different investigation methods: wind tunnel analysis, full scale experiments and computational fluid dynamics (CFD) to examine the physics of wind driven cross ventilation. Following the systematic approaches of the three methods, this study first conducted full scale measurements of wind properties, façade pressures, air flow rates through small window openings, and tracer gas concentrations in a multi-zone test house. Secondly, a scaled model of the test house was studied in a boundary layer wind tunnel (BLWT) for its façade pressures and ventilation rate under various wind incident angles. Finally, a CFD model of the test house was simulated under various constraints to determine the factors which affect indoor air distribution during wind driven cross ventilation events. The full scale experimental results showed a strong correlation between the cross ventilation rate and the wind velocity component normal to the inlet openings. This correlation suggested that the cross ventilation flow rate could be estimated from wind conditions alone. A closer examination of the wind characteristics also revealed that the cyclical pattern of changing wind direction could be impacted by obstructions which are kilometers upwind, suggesting that distant landscapes could have an impact on cross ventilation flows. The combination of CFD and full scale measurements also showed that local heat sources can generate significant buoyancy driven flow and affect indoor mixing during wind-driven cross ventilation scenarios. Experimentally validated parametric CFD analyses demonstrated the effect of interior heat loads in driving internal airflow, and suggest that a small source (35W/m2) can increase the indoor mixing from less than 1 ACH to 8 ACH between indoor spaces. Finally, the wind tunnel and CFD coupled analysis was found to predict the cross ventilation flow which was also validated against the full scaled measurements. The prediction, which may only be applicable to similar building types with small openings, showed significant agreement that such method has potential as an innovative design tool for natural ventilation in buildings. / text

Water availability is a common concern in semi-arid regions, such as Southern Arizona, USA. Hydroponic greenhouse crop production greatly reduces irrigation water use, but the study of water use by evaporative cooling has been limited.This project investigated water use by two evaporative cooling systems: pad-and-fan and high-pressure-fog with fan ventilation. All studies were performed in a double-layer polyethylene film-covered greenhouse (28 x 9.8 x 6.3 m) with mature tomato plants (2.9 plants m-2). Water use efficiency (WUE, kg yield per m3 water use) was calculated daily according to ventilation rate, as well as for a 6-month croppipng period, which used temperature-controlled pad-and-fan cooling.Pad-and-fan water use was 3.2, 6.4, 8.5, and 10.3 L m-2 d-1 for ventilation rates of 0.016, 0.034, 0.047, 0.061 m3 m-2 s-1, respectively. High-pressure-fog water use with a single central, overhead line was 7.9, 7.4, and 9.3 L m-2 d-1 for ventilation rates of 0.01, 0.016, 0.034 m3 m-2 s-1, respectively. For pad-and-fan ventilation rates less than 0.034 m3 m-2 s-1, total greenhouse WUE (20 - 33 kg m-3) was similar to field drip irrigation. For the temperature-controlled high-pressure-fog system, total greenhouse WUE (14 - 17 kg m-3) was similar to field sprinkler irrigation.For the 6-month crop cycle, combining water use by closed irrigation and pad-and-fan systems produced a total WUE of 15 kg m-3. Pad-and-fan WUE increased during monsoon conditions due to lower water use rates.Evaporative cooling water use and air temperature were well-predicted by the energy balance model. Predictions of air temperature improved when outside climate the measured conditions at one greenhouse location. Wind tunnel and full-scale studies of natural ventilation demonstrated the value of knowing airflow patterns when designing and operating a high-pressure-fog systemIt is possible for greenhouse tomato production to have a higher WUE than field production, if ventilation rates are not excessive, if closed irrigation is used, and if control methodologies are improved. Water use can be minimized by knowing how the evaporative cooling system affects greenhouse climate and plant responses.

The dynamics of controlled transitory 2- and 3-D attachment of the separated flow over a 2-D airfoil model are investigated in wind tunnel experiments. Pulsed actuation is effected on time scales that are an order of magnitude shorter than the characteristic convective time scale of the base flow by momentary jets that are generated by a spanwise array of combustion-based actuators. The effects of the transitory actuation on the aerodynamic characteristics of the airfoil are assessed using measurements of the global lift force and pitching moment and of streamwise distributions of surface pressure, and planar and stereoscopic particle image velocimetry (PIV) acquired phase-locked to the actuation waveform. A single spanwise-bounded actuation pulse leads to 2-D severing of the separated vorticity layer and the subsequent shedding of a large-scale stall vortex that are followed by momentary attachment of the upstream boundary layer and ultimately re-separation that are accompanied by a strong transitory change in the airfoil's circulation. It is shown that the primary mechanism for the attachment is alteration of the adverse pressure gradient of the separated base flow by local blockage of the momentary jet and.the formation of the large-scale stall vortex. The disparity between the characteristic time scales of flow attachment and subsequent separation [O(Tconv) and O(10Tconv), respectively] is exploited for temporal and spatial extensions of the attachment and enhancement of the global aerodynamic performance using strings of successive actuation pulses. Pulsed actuation effected by an unbounded actuator array leads to spanwise spreading of the induced transitory 3-D flow attachment well beyond the spanwise edges of the actuators. It is shown that 3-D pulsed actuation enhances the accumulation of vorticity over the airfoil and improves its aerodynamic performance compared to 2-D, spanwise-bounded actuation. When the airfoil is undergoing time-periodic pitch oscillations beyond its static stall margin, a sequence of staged 3-D actuation pulses coupled to the airfoil's motion can lead to reduced lift hysteresis and increased pitch stability (lower “negative damping”) that are typically associated with the presence of dynamic stall.

The short range dispersion in the atmosphere of buoyant gases, such as hot air or natural gas, may be hazardous and dangerous. The available methods for studying this problem were reviewed. Wind tunnel studies were considered to be the most suitable method for studying near-field dispersion, and methods for accurately modelling the nearfield behaviour of a buoyant plume of gas were examined. The experiments were performed in the Oxford University 4m x 2m low speed wind tunnel at a model scale of 1:200. The mean trajectory and rate of spread of a buoyant plume from a 60 m high (full-scale) stack were measured in the presence of a simulated natural wind. The exact similarity requirements were derived from dimensional analysis and from the equations of motion. In practice, it is not possible to match all the necessary dimensionless groups and exact scaling of the exit gas density ratio and the exit Reynolds number is often relaxed. A series of experiments was performed to examine the effect of these two groups on mean plume behaviour, with the intention of providing guidance for correct simulation of plume dispersion at reduced-scale. The exit density ratio was found to have little effect on the near-field plume behaviour, provided all the other dimensionless groups were matched. Plumes with low Reynolds number were found to rise significantly higher than plumes with higher 'turbulent' Reynolds numbers. This difference in trajectory could not be correlated with the plume exit momentum flux. The effect of the cross-flow on near-field dispersion was examined by performing experiments in four different simulations of the earth's atmospheric boundary-layer. The behaviour of the plume was found to be sensitive to both the velocity profile and the turbulence intensity of the cross-flow. To study dispersion in the wind tunnel, the cross-flow should be an accurate simulation of the velocity profile and turbulence intensity components of the natural wind.

The aerodynamics of bodies in compressible ground effect flowfields from low-subsonic to supersonic Mach numbers have been investigated numerically and experimentally. A study of existing literature indicated that compressible ground effect has been addressed sporadically in various contexts, without being researched in any comprehensive detail. One of the reasons for this is the difficulty involved in performing experiments which accurately simulate the flows in question with regards to ground boundary conditions. To maximise the relevance of the research to appropriate real-world scenarios, multiple bodies were examined within the confines of their own specific flow regimes. These were: an inverted T026 wing in the low-to-medium subsonic regime, a lifting RAE 2822 aerofoil and ONERA M6 wing in the transonic regime, and a NATO military projectile at supersonic Mach numbers. Two primary aims were pursued. Firstly, experimental issues surrounding compressible ground effect flows were addressed. Potential problems were found in the practice of matching incompressible Computational Fluid Dynamics (CFD) simulations to wind tunnel experiments for the inverted wing at low freestream Mach numbers (<0.3), where the inverted wing was found to experience significant compressible effects even at Mach 0.15. The approach of matching full-scale CFD simulations to scale model testing at an identical Reynolds number but higher Mach number was analysed and found to be prone to significant error. An exploration was also conducted of appropriate ways to conduct experimental tests at transonic and supersonic Mach numbers, resulting in the recommendation of a symmetry (image) method as an effective means of approximating a moving ground boundary in a small-scale blowdown wind tunnel. Issues of scale with regards to Reynolds number persisted in the transonic regime, but with careful use of CFD as a complement to experiments, discrepancies were quantified with confidence. The second primary aim was to use CFD to gain a broader understanding of the ways in which density changes in the flowfield affect the aerodynamic performance of the bodies in question, in particular when a shock wave reflects from the ground plane to interact again with the body or its wake. The numerical approach was extensively verified and validated against existing and new experimental data. The lifting aerofoil and wing were investigated over a range of mid-to-high subsonic Mach numbers (1>M???>0.5), ground clearances and angles of incidence. The presence of the ground was found to affect the critical Mach number, and the aerodynamic characteristics of the bodies across all Mach numbers and clearances proved to be highly sensitive to ground proximity, with a step change in any variable often causing a considerable change to the lift, moment and drag coefficients. At the lowest ground clearances in both two and three dimensional studies, the aerodynamic efficiency was generally found to be less than that of unbounded (no ground) flight for shock-dominated flowfields at freestream Mach numbers greater than 0.7. In the fully-supersonic regime, where shocks tend to be steady and oblique, a supersonic spinning NATO projectile travelling at Mach 2.4 was simulated at several ground clearances. The shocks produced by the body reflected from the ground plane and interacted with the far wake, the near wake, and/or the body itself depending on the ground clearance. The influence of these wave reflections on the three-dimensional flowfield, and their resultant effects on the aerodynamic coefficients, was determined. The normal and drag forces acting on the projectile increased in exponential fashion once the reflections impinged on the projectile body again one or more times (at a height/diameter ground clearance h/d<1). The pitching moment of the projectile changed sign as ground clearance was reduced, adding to the complexity of the trajectory which would ensue.

Football is widely regarded as the most popular sport in the world involving over 270 million people from different countries and cultures. It can be argued that the football is one of most important aspects of the game and hence the flight of the ball, if unexpected, can alter the outcome of the game. This thesis provides an engineering perspective and contribution to the continued understanding and improvement of the in-flight performance of FIFA approved footballs. Skilful players will impart spin onto a ball to induce a curve in-flight to try and deceive opponents. This flight is generally smooth, although subtle variations in the orientation and spin rate may cause conditions that affect the path and final ball position, in a manner considered to be unpredictable due to aerodynamic effects. Ball designs and manufacturing techniques are evolving and certain seam configurations are known to induce asymmetric pressure distributions resulting in lateral movement during flight. Aerodynamic research of sport balls has primarily focused on drag and the effects of high spin rates. Studies have shown the introduction of surface roughness affects the boundary layer state compared to a smooth sphere. Surface roughness on a football takes many forms including seam configurations and micro surface textures. The influence of changing the density, distribution and dimensions of the surface roughness with respect to the aerodynamic behaviour has been researched. The principle focus of this thesis is concerned with the influence on the lateral component as a result of applying surface roughness to the outer surfaces. The influence of the surface roughness on the drag and lateral components were determined using established wind tunnel techniques. Real balls and full size prototypes were tested. A mathematical flight model was employed to simulate realistic multiple flight trajectories based on empirical aerodynamic data. Mathematical and statistical techniques, including R.M.S and AutoCorrelation Functions were used to analyse the data. The results from this research showed how small variations in surface texture affected the complex nature of the lateral forces. Trajectories varied significantly depending on initial orientation and slow spin rate sensitivities. In conclusion, ball characterisation techniques were developed that identified lateral deviation and shape measures and considered a gradient profiling approach. Application of these novel parameters through multiple trajectory analysis allowed for an in-flight performance measure of footballs designs.