Dynamic stall characteristics of an NACA-0012 airfoil were investigated to assess the possibility of augmented lift during sinusoidal angle of attack motion. Tests were conducted over a range of Reynolds numbers from 2.0x10^5 to 5.0x10^5 and reduced frequencies from 0.02 to 0.3. The data were recorded and plotted in a series of lift coefficient vs. angle of attack diagrams. These diagrams exhibited a hysteresis curve for the dynamic stall cycle similar to the results of previous investigators but without a large peak at high angles of attack. The data were also plotted with lift coefficient vs. angular cycle position. The average lift coefficient was computed for each set of test conditions and plotted with average lift coefficient vs. reduced frequency for each value of Reynolds number. The summary data indicate an increase of average lift coefficient with reduced frequency, and increased Reynolds number, althought the increase was not monotonic.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Includes bibliographical references. / M.S.

In two-phase flow, the void fraction and its distribution are two major factors describing the characteristic of flow patterns. Better understanding of void fraction distribution in two-phase flow would help improve safety and efficiency in the nuclear industry as the heat transfer process is significantly affected by the void distribution in nuclear reactor fuel bundles. Lift force is proposed to explain the lateral migration of bubbles in the shear flow (Feng & Bolotnov, 2017, Lucas & Tomiyama, 2011, Akio Tomiyama, Tamai, Zun, & Hosokawa, 2002). However, the mechanism of lift force is unclear and the research on lift force is limited.<div><br></div><div>An experimental investigation is performed on the lift force of single bubble in weak linear shear flow field in water. In addition, characteristics of bubble motion including bubble terminal velocity, aspect ratio and oscillation amplitude are studied and comparisons are made with existing models.<br></div><div><br></div><div>It was found that the model proposed by Tomiyama et al. (A. Tomiyama, Celata, Hosokawa, & Yoshida, 2002) has the best prediction of bubble terminal velocity with introduction of a tuning factor in consideration of the asymmetric deformation of bubble. Bubble aspect ratio is found to significantly affect its terminal velocity, and a new model is proposed to best fit the experiment data. It is also observed that the shear rate magnitude has no influence on bubble aspect ratio in this study. Oscillation was observed for all the bubbles in this experiment. Oscillation amplitude scattered widely and it was difficult to correlate it only with the bubble equivalent diameter. In terms of lift force, positive lift coefficient was observed for small size bubbles and transits to negative value with growing size. Due to the high Reynolds number of flow and low viscosity of water, widely scattered data is found in the results. Although the accurate prediction of lift coefficient is difficult to obtain in the experiment, the lift coefficient transition trend is given and agrees with many other research. In addition, this research provides a database for further lift coefficient investigation.<br></div>

Visual analysis of an object's size can be used to determine the lifting forces we program to lift the object so that the resulting movements achieve the goals of the lift. These forces are scaled or specified prior to the object moving, that is, before sensory feedback information about the object's weight is available. Sensorimotor memories are relied on to provide relevant information about an object's density and weight if the object was previously manipulated. It is well established that young adults accurately scale their forces based on visual size cues. The purpose of this study was to determine if old adults scale their forces to the size of the object or if they rely on sensorimotor memory of the previous object's weight. There are reports of impaired visuomotor programing for grasp and lift in old adults. In the present study old and young subjects were required to lift four different sized bottles of constant density from a force plate and then place the object on a shelf. Two experiments were performed. Experiment one featured blocks of lifts for three bottles in the following order: large, small and medium. Experiment two took place fifteen minutes after experiment one and featured a bottle slightly larger than the medium bottle used at the end of the experiment one. The second experiment addressed whether imperceptible changes in size cause changes in predictive force scaling. Peak load force rate in the first force pulse (prior to lift-off) was measured for each lift of the objects with the focus being on the initial and last lift of each bottle. Both experiments presented a significant effect for bottle size on lift force rates. This result was found regardless of age. It provides additional support that young adults accurately scale their lift force rate based on the visual size cues of the object. Old adults also demonstrated scaling of their lift force rates based on bottle size which failed to support the hypothesis that old adults would merely reproduce their lift force rates from the previous lift with a different object. While both young and old scale lift forces to object size, the old demonstrated a trend for utilizing high lift force rates throughout the experiment as well as greater differences in lift force rate between the initial lift with an object and the final lift with the same object. Most subjects utilized a target strategy in which they produced a single peak lift force rate pulse. This is indicative of a neural representation of the weight of the object being utilized to program the lift force rate. The remaining subjects exhibited a probing strategy that features several step-wise increases in lift force rate until the object is lifted off. This represents a more cautious approach to lifting novel objects. Our results indicate that old adults, much like young adults, are able to scale their forces based on visual size cues.

There are numerous numerical and experimental studies to find correlations of octane rating with fuel properties. This thesis was based on the hypothesis that quenching characteristics at ignition locations impact the flame development. Conversely, determination of quenching characteristics might serve as an effective measure to determine the fuel mixture octane number. This hypothesis was tested with premixed flame experiments using primary reference fuels (iso-octane and n-heptane) and commercial grade gasoline. Premixed flame experiments were conducted on a flat flame burner. Primary reference fuels of different ratios were taken and correlated to their respective thermal quenching condition by introducing co-flowing inert gasses at room temperature with fuel-air mixture. The inert gasses that were used in the experiment are nitrogen and helium and the results are analyzed using a camera and an imaging spectrometer. The experimental results support the hypothesis that flame quenching can be correlated to fuel mixture octane number, and holds potential as an alternative method to determine the octane number.

This thesis covers some aspects of current aircraft design, and presents how experiment and simulation are used as tools. Together they give enhanced effects over employing either one separately. The work presented has been produced using both simulations and experiments. An overview of aircraft design tools is presented, together with a description of their application in research. Participation in two major design projects, HELIX and the Rescue wing, gave an opportunity to combine traditional experimental and computational tools. They also serve as a platform for developing two new tools, the vortex lattice program Tornado and the DoTrack camera based wind tunnel measurement system. The HELIX project aimed at exploring new, unconventional high-lift systems, such as blown flaps, flaperons and active vortex generators. The concepts were investigated with an array of conceptual design tools, ranging from handbook methods to high Reynold’s number wind tunnels. The research was done in several stages. After each stage the concepts failing to reach specifications were discontinued. The active vortex generator concept is followed in detail from the first phase in the HELIX project, and was finally evaluated by full computational fluid dynamics (CFD) and wind tunnel testing. The lessons learned in HELIX were applied to the Rescue wing project, where a kite balloon system for emergency localization was developed. The project is truly multidisciplinary, and both experiment and simulation had to be used in close conjunction. Lack of appropriate methods for measurement and analysis of this kind of device meant that new methods had to be developed. Recent experience of academia working closely together with industry has shown substantial benefits to all parties involved. The synergy of computer modeling and simulation with experiment plays an important role in the common collaborative modus operandi of academia and industry. In particular, the later stages of aeronautic educational programmes should actively pursue such collaboration. / QC 20100910

The purpose of this thesis is to give a preliminary investigation into the effect of wing deformation on flight dynamics. The candidate vehicle is FW-11 which is a flying wing configuration aircraft with high altitude and long endurance characteristics. The aeroelastic effect may be significant for this type of configuration. Two cases, the effect of flexible wing on lift distribution and on roll effectiveness during the cruise condition with different inertial parameters are investigated. For the first case, as the wing bending and twisting depend on the interaction between the wing structural deflections and the aerodynamic loads, the equilibrium condition should be calculated. In order to get that condition, mass, structure characteristics and aerodynamic characteristics are estimated first. Then load model and aerodynamic model are built. Next the interaction calculation program is applied and the equilibrium condition of the aircraft is calculated. After that, effect of wing flexibility on lift parameters is investigated. The influence of CG, location of lift and location of flexural axis are investigated. The other case is to calculate the transient roll rate response and estimate the rolling effectiveness of flexible aircraft, and compared with the rigid aircraft’s. A pure roll model is built and derivatives both for the rigid wing and the flexible wing are estimated. It has been found that flexible wing leads to the loss of control effectiveness, even cause reversal when reduces the structure natural frequency. The influence of inertia data for flexible roll is also investigated.

No description available.

Abstract Negative index structures could be implemented through surface Plasmon polariton waves generated by nanostructures. We are interested in PMMA grating structure on curved metal surface. In order to fabricate this kind of samples, a series process parameters have been tested and also the lift-off process has been developed. Our results show superlens effect under optical microscope(OM). The sub-wavelength grating image is reconstructed in the non-grating region where the PMMA dielectric layer is not uniform. Surface Plasmon(SPP) waves generated in the grating region propagate to the non-grating region and are scattered out through the non-uniform PMMA layer. The grating information is not resolvable under OM but clear in the reconstructed region. It shows that SPP waves can show super resolution and a simple batch process should be developed in the future.

Three flexure pivot pad bearings (FPBs) with different preloads are evaluated for use in high performance applications by comparing them to a hybrid hydrostatic bearing (HHB). One application of these bearings is in turbopumps for liquid rocket engines. To evaluate bearing performance, the lift-off speed of the shaft from the bearing surface is experimentally determined. Experimental data of lift-off are collected using a circuit running through the shaft and the designed bearing. Other methods for measuring liftoff speeds were attempted but did not yield consistent results. Water is used as a lubricant to simulate a low viscosity medium. In comparison to load-capacity-based predictions for FPBs, the experimental results showed lower lift-off speeds, higher load capacities, higher eccentricity ratios, and lower attitude angles. The bearings’ predicted load capacity determined lift-off speed predictions, but the experimental results show no clear trend relating lift-off speed to load capacity. This was for a range of running speeds, with the design speed defined as the final speed in a particular test case. At 0.689 bar supply pressure and for a design speed of 3000 rpm, the HHB showed greater load capacities and lower eccentricities than the FPBs, but the FPBs had lower lift-off speeds and attitude angles. In fact, the FPBs in the load-between-pad orientation outperformed the HHB in the load-on-pocket orientation with lower lift-off speeds for the shaft weight-only case. An increased supply pressure lowered the lift-off speeds in the HHB tests. If the load in the bearing application remains relatively small, a FPB could be substituted for an HHB.