Historically, the endeavor of scale testing flight vehicles at supersonic Mach numbers, especially for long durations, has required the development of closed-loop wind tunnels, which are extremely expensive both to build and operate due to the high complexity and incredible power required to drive such a system. The intermittent blowdown wind tunnel, indraft tunnel, and shock tunnel have alleviated many of these cost requirements to some degree, whilst facilitating testing at very high Mach numbers and enthalpies; however, these systems require the handling of gases at pressures and temperatures that can be prohibitive for many university settings. The Ludwieg tube provides a simple, elegant method for producing testable supersonic flows at price points significantly lower than the aforementioned test-system architectures. Unfortunately, the spacial footprint and moderate cost required for driver tube and nozzle hardware can make it difficult to implement for many non-research universities. In this thesis, a new supersonic test system architecture is conceived, designed, implemented, and validated for the purpose of making supersonic aerodynamic testing capability attainable for most universities, by combining properties of the Ludwieg Tube and indraft wind tunnel to reduce the cost needed to produce this capability. This system, the Indraft Tube Tunnel, requires no long driver-tube or test-section hardware, aside from a vacuum chamber. Furthermore, it is safe to operate, as high pressure containment systems are not required for the Indraft Tube Tunnel System. It is designed and operated to draw stagnant atmospheric air through a converging-diverging nozzle to achieve a steady-state Mach number of 2.5. Sufficient pressure ratio to reach the desired Mach number is attained by evacuating the vacuum chamber and placing a thin cellophane diaphragm across the inlet of the nozzle, thus separating the vacuum section from ambient atmosphere. To initiate gas flow, the diaphragm is mechanically burst with a puncture device. This design requires much less hardware to implement than a typical Ludwieg tube, and had an operating cost of less than one dollar per test. Using this method, steady, uninterrupted Mach 2.44 is attained for a duration of 13.6 ms and a test section diameter of 7 inches. The standard deviation of the Mach number measurements is .08 Mach. A shadowgraph imaging setup is used to view and measure the angle of oblique shockwaves on a simple wedge test-model. The Indraft Tube Tunnel is novel in the field of high-speed aerodynamic testing, and may be implemented by other universities to produce supersonic flows with a relatively small investment in hardware and laboratory space.

abstract: An airborne, tethered, multi-rotor wind turbine, effectively a rotorcraft kite, provides one platform for accessing the energy in high altitude winds. The craft is maintained at altitude by its rotors operating in autorotation, and its equilibrium attitude and dynamic performance are affected by the aerodynamic rotor forces, which in turn are affected by the orientation and motion of the craft. The aerodynamic performance of such rotors can vary significantly depending on orientation, influencing the efficiency of the system. This thesis analyzes the aerodynamic performance of an autorotating rotor through a range of angles of attack covering those experienced by a typical autogyro through that of a horizontal-axis wind turbine. To study the behavior of such rotors, an analytical model using the blade element theory coupled with momentum theory was developed. The model uses a rigid-rotor assumption and is nominally limited to cases of small induced inflow angle and constant induced velocity. The model allows for linear twist. In order to validate the model, several rotors -- off-the-shelf model-aircraft propellers -- were tested in a low speed wind tunnel. Custom built mounts allowed rotor angles of attack from 0 to 90 degrees in the test section, providing data for lift, drag, thrust, horizontal force, and angular velocity. Experimental results showed increasing thrust and angular velocity with rising pitch angles, whereas the in-plane horizontal force peaked and dropped after a certain value. The analytical results revealed a disagreement with the experimental trends, especially at high pitch angles. The discrepancy was attributed to the rotor operating in turbulent wake and vortex ring states at high pitch angles, where momentum theory has proven to be invalid. Also, aerodynamic design constants, which are not precisely known for the test propellers, have an underlying effect on the analytical model. The developments of the thesis suggest that a different analytical model may be needed for high rotor angles of attack. However, adding a term for resisting torque to the model gives analytical results that are similar to the experimental values. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

The dissertation thesis deals with short-term gas releases (puffs) in an urban canopy studied utilizing wind-tunnel modelling. The urban canopy was composed of buildings with pitched roofs organised into closed courtyards. Into it, a ground-level point gas source was placed. The first part of the thesis is focused on specific definitions of puff characteristics. New definitions of puff arrival and departure times are presented. Various definitions of puff arrival time were applied on the same datasets and the results were compared. Moreover, it was studied how slight changes in determination of puff departure time can affect its values and other derived puff characteristics. The second part of the thesis is focused on modelling of probability density functions of puff characteristics with knowledge of sampling positions towards the gas source and mean values of concentrations valid for long-term gas sources. The found equations will be utilized in an operational model. The outputs in the form of the probability density functions of puff characteristics distinguish my model from the usually utilized operational models, in which only the ensemble-averaged puff outline and concentration field can be predicted.

<div>Hypersonic flows consist of harsh environments where chemistry effects are relevant and low speed assumptions such as the ideal gas law and the continuum hypothesis</div><div>begin to break down. Because of these processes, computer models do a poor job of predicting behavior of vehicles in hypersonic flight. High fi?delity ground test</div><div>measurements are necessary to anchor and extrapolate CFD simulations so that flight vehicle designs can continue to improve. Due to the harsh conditions and complexities</div><div>of test facilities, implementing experimental measurements can prove challenging. Molecular tagging methods such as Femtosecond Laser Electronic Excitation Tagging</div><div>(FLEET) are attractive for use in hypersonic ground test facilities for many reasons. They are generally considered non-intrusive, since they require no physical probes or seed particles to be placed in the flow. This both keeps the facility safe from damage and minimizes the disturbance imparted on the flowfi?eld by the measurement. Since the tracer is comprised of molecules already present in the flow, the measurement is reliable and can track velocities over a wide dynamic range. The optical arrangement for FLEET is rather simple, requiring only a focused laser beam and a camera to capture the signal. The method can even be applied as a one-sided measurement requiring only one direction of optical access. The current state-of-the-art for the FLEET method is point-wise measurements made at 1 kHz with a</div><div>commercially available laser system. The basis for this thesis is to identify and address current limitations in the implementation of FLEET to relevant flow facilities in terms of the useful aerodynamic information that can be extracted. Fundamental advances to the spatial extent and temporal resolution of FLEET are investigated, and novel applied measurements in high speed flow facilities are presented. Considerations of the precision, spatial resolution and ability to implement fundamental advances to harsh and more complex environments are discussed. A custom-built burst-mode femtosecond laser system is used to enable FLEET measurements at 1 MHz, an improvement of three orders</div><div>of magnitude in measurement rate. New optical arrangements including microlens arrays and holographic beamsplitters are developed to allow multi-dimensional grids</div><div>to be tracked to instantaneously measure velocity gradients. Shock wave and shear measurements in a supersonic bladeless turbine and boundary layer measurements</div><div>on a Mach 6 cone-cylinder-flare are demonstrated. Additionally, an adapted method, Femtosecond Laser Activation and Sensing of Hydroxyl (FLASH) is developed and applied to measure velocity in reacting environments such as a Rotating Detonation Engine (RDE). These innovations provide a path forward for improving the spatiotemproal fi?delity of velocity measurements and extending the capability for investigation high-speed reacting and non-reacting flows in hypersonic ground test facilities.</div><div><br></div>

<div>To perform high spatial resolution measurements on the characterization of a Surface Air-Cooled heat exchanger a suitable empirical procedure and a novel wide range traverse system have been defined.</div><div>The characterization through transient measurements involves a proper-sized test article with an array of electric resistances. These provide an accurate and controlled adjustment of the heat provided to the fin array and a fast interruption of the power delivered. A series of numerical simulations were performed on this warm-up state to ensure a homogeneous temperature field throughout the model, and results indicate a mutual constraint from adjacent fins in their respective ability to dissipate heat. Additionally, a large number of pressure taps, with a time response of 0.28 seconds, were distributed throughout the study array to capture and validate the pressure regions provided by numerical simulations that correspond to flow expansions and growth of horseshoe vortices. The test section was also supplemented with accurate RTD sensors to validate the simulated temperature fields, as well as other optical techniques to capture aerodynamic and thermal effects during the test campaigns.</div><div>To supplement the high-spatial-resolution measurements, a novel traverse system has been designed. This one combines the independent motions of a rotating disk and the translation of the plate containing such disk to locate a probe all over an unprecedented wide area in an uninterrupted way. A proper sealing was achieved through standard O-ring seals and the introduction of two custom chambers at the test section sides. The action of these seals led to the proper power selection for this mechanism. Finally, a series of Finite Element Analyses assessed the structural integrity of the proposed traversing system and defined its pressure performance map from vacuum to 6 [bar] in the test section.</div>

<p>Highly loaded aerodynamic devices for propulsion and power generation are emerging to increase power output in a more compact machine are emerging. These devices can experience increased losses due to separation, as in the low-pressure turbine, which arise due to the operation at conditions that increases the adverse pressure gradients ore decrease the Reynolds number of the flow through the device. Therefore, flow control strategies become appealing to reduce losses at these conditions. This work aims to validate flow injection as an effective flow control strategy in the transonic regime.</p> <p>A test facility which was used to study boundary layer separation in a quasi-2d test article was modified to include flow injection and conditions were modified so that the facility was operated in the transonic regime. Valves were chosen which could achieve a wide range of excitation frequencies and the flow control ports were designed to accommodate their nominal flow rate. A preliminary test matrix was built while considering the limitations of the test facility.</p> <p>A numerical study was conducted to identify flow structures of interest and determine a preliminary understanding of the test article. The flow control was then added to the numerical study to guide the experimental set points for injected flow. The response of the flow to continuous slot blowing was characterized, and a 3D simulation with discrete injection ports was done to ensure the set-points determined from the 2D study were viable for discrete injection.</p> <p>Blow-down experiments were then conducted to study the behavior of bulk separation in a transonic regime for a quasi-2D geometry. Once behavior of the separation was understood, steady injection and then pulsated injection were applied in attempts to mitigate the separation. Steady injection was utilized to find the required pressure of injection relative to the total pressure at the inlet of the test article, while the pulsated injection served to identify a frequency at which the time averaged mitigation of separation was greatest.</p> <p>The experiments show that both steady and pulsated flow injection are viable techniques in flow control. It is also shown that pulsation does not allow for a lower pressure injection, but instead allows for the same effect with a lower mass flow requirement. Two-dimensional computational simulations are shown to be effective in determining injection frequencies but not the extent of separation or required injection pressures.</p>

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The aim of this licentiate thesis is to investigate wind-turbines placed in a complex-terrain environment. This is done by studying the flow around small-scale wind-turbine models placed over a landscape model with hills, and by comparing the results with corresponding data obtained over a flat terrain model. The studied flow features include the wind-turbine wake development and the turbine performance under different conditions, the effects from wake interactions, the influence of the ambient turbulence levels and the influence from a complex topography. Wind-tunnel measurements have been performed using particle image velocimetry and hot-wire anemometry to measure the velocity field. Additionally, numerical simulations, based on RANS modelling and actuator-disc techniques, have been made to support the experimental data and to gain further knowledge about the investigated flow cases. The results reveal that the hills promote a downward wake deflection behind the turbines and enhance the wind-turbine wake diffusion. As a consequence of this, and with the flow acceleration introduced by the hills, an improved power performance is seen for turbines exposed to wake-interference effects. A correlation is observed between the turbulence levels present in the flow, and the magnitude to which the hill-induced flow gradients influence the wake: Stronger wake deflections due to the hills are seen when the wind-turbine wake is more diffused. This is for instance the case when the wake of two tandem turbines is studied, or when higher ambient turbulence levels are present in the wind tunnel. A good qualitative agreement is seen when comparing the experimental and numerical results. The simulation results further indicate that the hills give rise to modulations of the wind-turbine wake. It is shown that these modulations can be reasonably captured by means of wake-superposition techniques, given that a wake model with sufficient accuracy is chosen. / Syftet med denna licentiatavhandling är att öka förståelsen om hur vindturbiner påverkas av en omgivande komplex terräng. Huvudsakligen betraktas luftströmningen kring småskaliga vindturbinsmodeller som placerats över en landskapsmodell med kullar. I tillägg görs jämförelser med resultat som erhållits då vindtubinerna placerats över en platt landskapsmodell. De studerade strömningsaspekterna inkluderar vindturbinernas vakutveckling och prestanda under olika förhållanden, inverkan från vakinteraktioner, inflytande från omgivande turbulensnivåer och inverkan från en komplex topografi. Vindtunnelmätningar har utf ̈orts där PIV och varmtrådsanemometri användes för att uppmäta hastighetsfält. I tillägg har numeriska simuleringar utförts baserade på RANS-modellering, där turbinens rotor beskrevs av en porös skiva. Simuleringarna gjordes som komplement till de experimentella mätresultaten för att få en ökad förståelse om de undersökta strömningsfallen. Resultaten från mätningarna och simuleringarna med kullar visar att terrängvariationerna främjar en nedåtgående vakförskjutning bakom turbinerna och ökar vindturbinernas vakdiffusion. Detta, i kombination med luftens acceleration över kullarna, resulterar i att en högre effektprestanda utvinns från en vindturbin vars inströmmande luftflöde störs av vaken från en framförliggande turbin. Vidare observeras kraftigare nedågående vakförskjutningar på grund av det kullriga landskapet då vindturbinsvakarna är mer diffunderade. Detta är exempelvis fallet då vaken bakom två turbiner placerade i en tandemkonfiguration studeras, eller när höga omgivande turbulensnivåer uppmäts i vindtunneln. En bra kvalitativ överensstämmelse kan ses mellan de experimentella och numeriska resultat som uppnås. Resultaten från simuleringarna indikerar dessutom att landskapet med kullar ger upphov till moduleringar av vindturbinens vak. Det visas att dessa moduleringar kan beskrivas någorlunda väl med hjälp av vaksuperpositionsmetoder, givet att en vakmodell med tillräckligt hög noggrannhet väljs. / <p>QC 20180122</p>

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