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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Open-wheel aerodynamics : effects of tyre deformation and internal flow

Sprot, Adam Joseph January 2013 (has links)
Competitive performance of an F1 race car relies upon a well designed and highly developed aerodynamic system. In order to achieve this, total understanding of the downstream wake of exposed rotating wheels is essential. Components such as bargeboards and indeed much of the front wing are developed to provide pressure gradients and vortex structures to influence the wheel wake, ensuring high energy mass-flow to the sensitive leading edge of the underfloor and eventually the rear wing. Wind tunnel testing of model-scale deformable tyres has become a common occurrence in F1 in recent years although there is a significant lack of available literature, academic or otherwise, as to their use. This work has studied in detail the aerodynamic consequences which occur from the varying sidewall bulge and contact patch region making use of several techniques. These include scanning rotating tyre profiles under load, static contact patch size measurements, five-hole pressure probe wake measurements, particle image velocimetry (PIV) and load-cell drag measurements. CFD simulations utilising two industrial codes have also been performed to support the experimental work. Coordinates representing tyre profiles under a range of on-track conditions are available for other researchers to use as a basis for CFD studies. The work presented here includes a full range of representative on-track axle heights which far exceed the more conservative range usually tested in an industrial setting for longevity reasons. The most sensitive parameters for aerodynamic testing of wheels have been identified. For development of a full car, in decreasing order of priority, the following must be correctly matched to the realistic scenario: axle height, yaw condition (without glycerol - often used to reduce friction at the expense of a compromised tyre profile), camber angle, detailed internals, high inflation pressure, through-hub flow rate and least significantly the rotation of the internal brake rotor. The study of through-hub flows revealed that the external aerodynamic effect of the brake scoop inlet varies significantly with the amount of internal restriction. The pumping effect of the brake rotor was measured to be negligible compared to the restrictive effect of its internal passages and that leads to an effect known as inlet spillage with a negative cooling drag trend, whereby the drag of the wheel assembly decreases with increased through-hub flow.
32

Field research in flying training

Frisby, C. B. January 1947 (has links)
No description available.
33

A quantitative investigation of the effects of motion on an aircraft simulation

Ekin, William Holland January 1977 (has links)
No description available.
34

Fluid-structure interaction of membrane aerofoils at low Reynolds numbers

Serrano Galiano, Sonia January 2016 (has links)
This thesis investigates the fluid-structure interaction (FSI) problem of elastic membrane aerofoils at low Reynolds numbers. The dynamics of the fluid and membrane coupled system is studied via direct numerical simulation (DNS) using a newly developed computational framework whose characteristics and validation are included in this report. A set of two-dimensional DNS were performed for varying Reynolds number, membrane elasticity and aerofoil geometry in order to investigate the effect of these relevant fluid and structural parameters on the behaviour of fluid-structure coupled system. Static and dynamic features of the system, and their effect in aerodynamic properties, are described and compared for the different parameter combinations. The case with highest Reynolds number, Re = 10; 000, and intermediate elasticity was chosen as a base case to further study the fluid-structure coupling mechanism, particularly at low angle of attack conditions. The dynamic behaviour was characterised via spectral analysis in the frequency and wavenumber-frequency domains, which allowed the propagating wave nature of the membrane vibrations and their effect on the surrounding pressure field fluctuations to be clarified. The membrane vibrations are found to introduce upstream-propagating pressure waves that seem to be responsible for a loss in aerodynamic efficiency compared to a rigid aerofoil. Stability aspects of the FSI problem are also investigated by performing numerical experiments to analyse the response of the system to initial flow perturbations. The solutions of the 2D DNS are used as initial conditions for three-dimensional simulations, upon which initial perturbations in spanwise velocity are added. As the simulation is advanced in time the evolution of the perturbations is studied to determine the stability characteristics of the flow. Amplifications of the perturbations are found for Re > 10; 000. The coupling of the fully three-dimensional developed flow and the elastic aerofoil is also analysed with spectral techniques. Comparison of two- and three-dimensional results reveals that the three-dimensional flow development causes a decrease in the amplitude of the system fluctuations, but the same coupling mechanism found in the two-dimensional approach is also present in the three-dimensional case.
35

Gust load alleviation exploiting structural nonlinearity

Gai, G. January 2017 (has links)
Gust interaction is a crucial design consideration for civil aircraft. A gust disturbance is defined as any air velocity component normal to the flight path. Gust interactions can rapidly change the aerodynamic forces acting on a wing and in turn the loads on the aircraft. Indeed, during this interaction, the structure of the aircraft may experience significant dynamic loading. It is therefore desirable to utilise gust load alleviation systems in aircraft design. This thesis investigates the influence of nonlinear structural behaviour in aeroelastic systems for gust load alleviation. In conjunction to the study of nonlinearities in structures, numerical methods for the fast prediction of stability and dynamic response for the nonlinear aeroelastic systems are required. To this end, this thesis investigates the nonlinear model order reduction framework based on eigenmode decomposition. The nonlinear model reduction approach based on eigenmode decomposition is formulated and extended to include expansion terms up to fifth order such that higher-order nonlinear behaviour of a physical system can be captured. The method is first applied to a two degree-of-freedom pitch-plunge aerofoil structural model in unsteady incompressible flow. Structural stiffness nonlinearity is introduced as a fifth-order polynomial, while the aerodynamics follow linear theory. It is demonstrated that the reduced-order model is capable of accurately capturing the nonlinear aeroelastic behaviour arising from gust excitation. Furthermore, an analysis of the computational cost associated with constructing such reduced-order model and its applicability to more complex aeroelastic problems is provided. The model reduction approach is then extended for a full-scale passenger aircraft exhibiting geometric structural nonlinearity. A structured approach to identify the dominant modes required to construct an accurate reduced-order model for such nonlinear aeroelastic system is presented. The effect of structural nonlinearities are studied through time domain gust response calculations and the reduced order model results are compared against the full-order reference solution. It is demonstrated that both the linear and nonlinear reduced-order models are capable of accurately predicting the dynamic gust response of aircraft structures while achieving significant reduction in system size.
36

Computational aerodynamics for open rotor tip vortex interaction noise prediction

Elson, Tom January 2015 (has links)
Open rotor engines can provide fuel savings of up to twenty seven percent compared to a modern high bypass turbofan engine. They were subject to intense research in the 1980s in response to the 1973 oil crisis. They have come back into consideration to combat the strict environmental regulations currently imposed on the aviation industry and to meet the ACARE 2020 requirements. Recent large scale European projects such as DREAM and Clean Sky have included signi cant research on the open rotor since their comeback. Their major drawback is the noise levels generated when the wake and tip vortices of the front rotor interact with the aft rotor. The noise generated from these interactions is highly tonal which makes the open rotor prohibitively noisy. The Unducted Fan (UDF) demonstrator engine was built in the 1980s by General Electric in collaboration with NASA. During the design phase of this project a computer code named CRPFAN was developed to predict the noise of open rotors. CRPFAN is used as a representative preliminary design noise prediction tool and was the only representative tool available to the author at the time of the project. Included in CRPFAN is a vortex model which relies heavily on outdated empirical re- lations. There is currently a better knowledge of tip vortex properties relative to when the code was created. However, there has been no signi cant study on how the speci c parameters of a tip vortex relate to the noise of an open rotor or how to more accurately predict the tip vortex parameters, which is what this project aims to do. The rst part of the project developed methods to quantify how the tip vortex param- eters relate to the noise generated by its interaction with the aft blade row. The next step was to further develop the state of the art of tip vortex models. This is done using basic analytical models integrated into CRPFAN and the use of Computational Fluid Dynamics (CFD) to model the tip vortices. CFD was used to develop bespoke tip vortex correlations which relate the tip vortex parameters to the open rotor performance parameters such as the lift, thrust and power coe cients. Correlations for the tip vortex axial velocity, trajectory, circulation and core size have been developed and integrated into CRPFAN with a detailed analysis of their performance relative to the current state of the art included. This thesis includes recommendations to improve the tip vortex models such as taking into account the spatial orientation of the vortex, inclusion of a vortex axial velocity component and how strip theory codes can under predict the noise.
37

Optimisation of the aircraft Cost Index for air travel emissions reduction

Edwards, Holly Alice January 2015 (has links)
The aviation industry is facing a tough challenge to achieve carbon neutral growth from 2020. The industry’s emissions continue to grow at a substantial rate, spurred by a 5% per annum increase in demand and a lack of large scale solutions to reduce its dependence on oil. A promising mitigation measure is the use of the Cost Index (CI) tool, its purpose being to balance the cost of time and the cost of fuel. The faster the flight, the more fuel is used and therefore costs increase. However, slower flights increase time-dependent costs, such as crew and maintenance costs. The CI value is entered into the aircraft flight management system to determine the speed of the flight. Analysis from this thesis reveals that CI could result in emissions savings of at least 1% on a flight-by-flight basis, comparable with other measures that can be implemented in the short-term. However, evidence suggests that airlines are currently misusing or miscalculating their CI values, resulting in higher costs and emissions. The aim of this thesis is to develop a novel method of calculating CI to make it practical and easy to use for airlines on a day-to-day basis. This was done by undertaking multiple CI calculations for different flight parameters and finding the CI value which minimises costs. This takes into account time-dependent costs, fuel costs and any carbon pricing to be applied, as well as any costs relating to passenger delay. The model also has a dual purpose of helping in the understanding of future impacts on an individual flight basis. It is found that in general the CI follows trends in jet fuel costs. However, when delay is added this has the most significant impact on the CI. Conversely, the addition of a carbon price, which is a key policy strategy in the industry to reduce emissions, had a negligible effect on the CI and resulting emissions. Future policy will need to recognise that these flight-by-flight interactions are important in order to find solutions that lead to meaningful CO2 reductions in the industry.
38

Aerodynamics of biplane and tandem wings at low Reynolds numbers

Jones, Robin January 2016 (has links)
Overcoming the difficulties associated with low Reynolds number flows has recently become a primary goal for aerodynamicists due to the growing importance of micro air vehicles (MAVs). The limiting size requirement of a six-inch wing span for MAVs combined with their inherent tendency to suffer stall due to gusts makes this significantly more challenging. The use of two-wing configurations, inspired by historical aircraft, could prove to be an effective method of overcoming this limitation. This thesis is primarily concerned with the fundamental aerodynamics associated with biplane and tandem wing configurations at a low Reynolds number using experimental evidence. Experiments were performed at a Reynolds number, based on wing chord, of Re = 10^5 in a return-circuit open-jet wind tunnel. The wing models were rectangular flat planform wings with a semi-aspect ratio of two. The effects of streamwise and crosswise wing separation, spanwise wing flexibility, angle of attack and decalage (the relative incidence of two wings) are considered. Experiments considering the effects of streamwise and transverse wing separation in rigid wings without decalage revealed that at post-stall angles of attack, lift performance improves and stall is delayed significantly for many two-wing configurations. For a given angle of attack, there are optimal transverse wing separations for which total lift coefficient is maximised. Particle image velocimetry (PIV) measurements reveal five characteristic flow regimes. The aerodynamic characteristics of two-wing configurations depend heavily on the nature of the accelerated inter-wing flow. This accelerated flow has a profound influence on the separated shear layers emanating from the leading and trailing edges of both wings. Unsteady forces intensify for certain two-wing configurations. High flow unsteadiness and large lift fluctuations are associated with either a switching between stalled and unstalled states over the trailing-wing's suction surface or a switching between merged and distinct wing wakes. Combinations of spanwise flexible wings with rigid wings for two streamwise wing separations, ΔX/c = 0.5 and 1.5, at an angle of attack of 30° were investigated with force measurements. The selected data compare rigid-leading rigid-trailing (R-R) wing configurations with flexible-leading rigid-trailing (F-R) wing configurations for ΔX/c = 1.5 (α = 30°). The transverse wing separation was varied systematically from -1.5 to 1.5 chord lengths. PIV, Digital Image Correlation (DIC) and hot-wire measurements were performed to further investigate the nature of these two cases. For the F-R case, transverse wing separations between 0.0 and 0.4 chord lengths exhibit increased lift coefficients relative to the R-R case; the main benefit in lift generation is for the trailing-wing. For the F-R configuration, spanwise deformation of the leading-flexible wing shifts the impingement point of the trailing-edge shear layer on the trailing-wing thus affecting lift generation. DIC measurements show that the presence of the rigid-trailing wing has a profound influence on the flow-induced vibrations of the leading-flexible wing. These flow induced vibrations reach the greatest amplitude at a transverse separation of 0.32 chord lengths, matching the largest unsteady forces. Hot-wire velocity spectra measurements reveal that cases producing increased unsteady forces possess distinct inter-wing velocity fluctuations which are coupled with the wing vibrations. The results demonstrate that the time-averaged forces and unsteady fluid-structure interactions are strongly determined by the crosswise wing separation and the spanwise flexibility of the leading-wing in tandem configurations. To investigate the effects of decalage (differing wing angle), experiments were performed for three cases in the stalled regime. Force measurements demonstrate that the use of decalage can strongly enhance the lift characteristics of two-wing configurations in the stalled regime. PIV measurements show that performance relies heavily on the augmentation of downwash and the occurrence of a secondary trailing edge recirculation region. Configurations producing enhanced aerodynamic and power efficiency are associated with reduced recirculation regions and increased downwash. Configurations yielding enhanced lift characteristics are associated with increased downwash as well as significant entrainment of the wake over the upper/leading wing due to the accelerated inter-wing flow. The stall of the upper/leading wing is consistently coupled with a secondary recirculation region due to the upper/leading wing's trailing edge shear layer. A significant transverse wing separation dependence occurs for a fixed leading wing incidence of 25° and trailing wing incidence of -10°. A very sharp discontinuity in time-average force coefficients between ΔY/c = -0.75 and -0.6 occurs for this case and a similar discontinuity is observed for a trailing wing incidence of -5°. Flow fields reveal a sensitive flow regime transition which is highly dependent on the transverse wing separation. Three configurations with increased unsteadiness were identified in the force data; instantaneous PIV measurements reveal subtle and intermittent inter-wing flows encroaching through the wake. Significant unsteady forces are only found to occur in the considered configurations (with decalage) when the wings' wakes are merged.
39

Aerodynamic characteristics of wide bleed slots

Matthews, R. D. January 1974 (has links)
The aerodynamic characteristics have been studied of a wide bleed slot in the presence of a terminal shock wave in a simulation of the bleed arrangements employed at the throat of some external compression intakes on supersonic aircraft. The problem was to investigate the nature of the flow field above the slot and to determine the governing flow mechanism. A comprehensive series of measurements, together with a theoretical study of the essentially inviscid nature of any shock wave/free shear layer interaction have led to the formulation of an inviscid model of the flow field which exhibited the correct relationship between primary flow, bleed flow, shock geometry and cavity pressure. The bleed flow itself is contained in the shear layer which emanates from the front lip and separates the high speed primary flow from the nearly stagnant air in the void. An experimental exploration of the shear layer was also carried out and the shear layer properties were incorporated into the inviscid model to give estimates of bleed flow total pressure immediately prior to its entry and diffusion into the bleed cavity. This has given a realistic criterion on which to base estimates of bleed diffusion efficiency.
40

Aerodynamic loads on slender wings in unsteady motion measured by a new technique

Cadwallader, R. January 1975 (has links)
An experiment has been performed to demonstrate the use of a new technique for measuring the unsteady longitudinal derivatives of slender wings at low speeds. The technique used a stationary fluid medium, water, and a model wing was towed through the water with its flight path constrained to follow a fixed cam rail. The normal force and pitching moment on the wing were measured by strain gauges fixed to its sting support. The new technique had the following advantages over traditional oscillatory methods: (i) The ratio of aerodynamic forces to inertia forces was high because water was used as the fluid. (ii) It was able to discriminate the w, q and theta derivatives. (iii) Any non-linearity in the derivatives could be studied without interference of transient effects. The longitudinal derivatives zw, zq, ztheta , mw, mq, mtheta for the AGARD model G planform were measured but there was a good deal of experimental scatter, particularly in the z derivatives. The m derivatives compared well with results from oscillatory tests but the z derivative did not compare so well. A correlation was obtained between the theoretical virtual mass and the transient behaviour of the normal force at the start of the plunging and constant q manoeuvres. The derivatives which cannot normally be measured independently, zq and m q, were measured to a better degree of accuracy than the other derivatives. Photographs of the paths of the vortex cores were obtained using the hydrogen bubble technique. The photographs were not of sufficient accuracy to enable a correlation to be made with the strain gauge measurements but a difference in the position of the vortices for positive and negative pitching rates was observed. It was concluded that the new technique could be successfully applied to the measurement of the derivatives for a slender wing but that modifications would be necessary to improve the precision of the measurements.

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