Thesis: M.S., Massachusetts Institute of Technology, Department of Aeronautical Engineering, 1932 / Includes bibliographical references. / by Charles Wilfred Crossland. / M.S. / M.S. Massachusetts Institute of Technology, Department of Aeronautical Engineering

Thesis: M.S., Massachusetts Institute of Technology, Department of Aeronautical Engineering, 1936 / Includes bibliographical references (leaves 68-70). / by Stanislaw A. Shumowsky. / M.S. / M.S. Massachusetts Institute of Technology, Department of Aeronautical Engineering

Thesis: B.S., Massachusetts Institute of Technology, Department of Aeronautical Engineering, 1943 / Includes bibliographical references (leaf 12). / by Ernest M. Spear. / B.S. / B.S. Massachusetts Institute of Technology, Department of Aeronautical Engineering

A turbulent boundary layer experiencing a time mean adverse pressure gradient and a controllable travelling wave periodic oscillation, was examined experimentally. An open return low speed wind-tunnel with a semi-open working section was used for this purpose, with oscillating flaps at its exit inducing the oscillations. The boundary layer on a specially designed "S" shaped model of chord 2m and thickness/ chord ratio of3.6%was investigated, for a range of frequencies from 1 to 6Hz, and amplitudes of the order of 10% of the time mean freestream velocity. The turbulent boundary layer evolved naturally around x/c= . 23, and measurements were taken for a Reynolds number Rec=3401. The effect of flap amplitude was examined for a range of amplitudes, from 2 to 4 inches. Unsteady velocity and pressure quantities were measured using Hot-wire techniques and pressure transducers, with the aid of a digital sampling system. Boundary layer mean values, were found to be invýriant with both frequency and amplitude of oscillation, while unsteady components were predominantly affected by frequency and downstream position but not amplitude. Unsteady velocities in the boundary layer lagged the freestream oscillations by as much as 1500 in some cases, while amplitudes exceeded freestream values by as much as 70%

A theoretical and experimental study is made of the closed 'bubbles` of separated flow formed when a laminar boundary layer separates from an aerofoil surface and, after undergoing transition to turbulence, subsequently re-attaches. Attention is mainly confined to the so-called 'short' type of bubble, which is distinguished from the 'long' type by its relatively slight overall effect upon the pressure distribution. In Part I, a semi-empirical theory for the prediction of the growth and bursting of two-dimensional short bubbles is developed. The existing data concerning short bubbles are re-examined, with particular emphasis upon the conditions governing re-attachment. A criterion for the determination of turbulent re-attachment is proposed, and approximate quadrature methods developed for the calculation of the momentum thickness in the separated region. These results, together with am empirical formula for the determination of the position of transition, are combined with a simplified model of the pressure distritbution in the bubble region to predict the re-attachment position. It is found that, for a given imposed pressure distribution, there exists a Reynolds number at separation below which re-attachment is impossible. This is associated with the phenomenon of short bubble bursting. The predictions of the theory are in reasonable quantitative agreement with experiment. Part II deals with bubbles in three-dimensional flow. Experiments are described in which separation bubbles were produced using an apparatus closely simulating conditions near the leading-edge of a swept wing of infinite span. Measurements of surface pressure, mean velocity and turbulence level are presented, from which it is deduced that the bubble structure is similar to that of two-dimensional bubbles, apart from the existence of cross-flows in the shear-layer and a strong spanwise flow in the reverse-flow vortex. An extension of the two-dimensional bursting theory by means of the independence principle is in reasonable agreement with measured bursting parameters.

An experimental investigation into the structure of the plane jet in a moving airstream has been made. The majority of the measurements have been made in a jet exhausting into a slow moving airstream providing an example of a possible self-preserving flow. The experiments showed that the flow does, in fact, become self-preserving at distances downstream from the jet nozzle of thirty jet nozzle width. The distributions of the turbulent intensities across the jet in the self-preserving region of the flow are shown to be similar to those found in the plane wake. However, the turbulent energy balance for the two flows appears to be quite different. Some measurements of the eddy structure indicate that shear carrying eddies are among the largest eddies in the flow and are also partly responsible for the intermittency phenomenon. The unsteady irrotational flow outside the jet is shown to be adequately described by the theories of Phillips (1955) and Stewart (1956). Some comments are made on the applicability of the various simple theories of turbulence to the plane jet and the interesting, though not necessarily significant, point emerges that the Prandtl Mixing Length theory gives the beat description of the flow structure. Additional measurements in jets in fast moving airstreams show that the change from a jet to a wake type of turbulence structure takes place at a very slow rate. Several simple theories were developed to account for the spread of a plane jet in a moving airstream but none of then proved wholly adequate. Apart from the main investigation, some work on the problem of measurements in a turbulent flow in discussed. Aspects of both hot wire anemometer theory and static pressure measurements are re-appraised.

The technique of microwave . limb sounding -from space represents a very powerful tool for determining the atmospheric processes involved in ozone depletion, the greenhouse effect, acid rain, etc.. Unfortunately, the technology involved in producing millimetric and submillimetric devices is highly complex, and miniature. The power levels and environmental conditions existing aboard spacecraft in present 'use, 5 differ from those required by the low noise heterodyne receivers employed by the Radio Astronomy community. Therefore, great effort has been spent in the design of radiometers with limited power and weight requirements, so that they can withstand the rigours of launch and operation in space. This thesis describes the design and construction of a subharmonically pumped, double diode mixer which is now used in an airborne atmospheric radiometer. The mixer power requirement and rugged nature make it an ideal option for space operation. The assembly of the millimetric circuit required the development, of novel techniques which enabled the incorporation of discrete circuit elements onto a single quartz substrate. This allowed the physical testing of the millimetric circuit independently of the RF block. A detailed investigation into the `whiskering' technique was carried out. It was thus possible to pinpoint errors that had previously occurred in assembly and which had resulted in the failure of a space flight device. With the adoption of quantified procedures, devices constructed using the `whiskering' technique were shown to be considerably more resilient than had previously been thought. The performance of the mixer is comparable with other designs using Schottky diodes at room temperature (-1200K DSB) and the local oscillator power requirement is easily met with a single solid state source. A simple theoretical analysis using the Seigel and Kerr program was undertaken in conjunction with RF measurements performed on a 65X scale model to determine steps required for further improvement.

A study has been carried out of the aerodynamic interference flow arising at the junction of a swept-forward wing, which is cambered, but without taper or twist and a flat plate on which a fully-developed, turbulent boundary layer approaches the junction. Initial CFD predictions of the pressures over the wing were carried out by the author at BAe, Hatfield. Flow visualisation tests and surface pressure measurements over the wind tunnel model were conducted at wing incidences from -3' to +9'. With the wing at 0' incidence, a single-tube yawmeter was used to explore the flow field around the leading-edge of the junction and an X-wire anemometer to examine the mean velocity and turbulence fields in the streamwise corners and at the trailing edge. The Reynolds number of the tests, based on the streamwise chord and free stream velocity of 30 m/s, was 1.03 A06. At low incidence,, a very weak separation occurred in the plate boundary layer, a very short distance upstream of the junction. However the oncoming stream converges into the junction, appearing to confine any vortical motion at the leading edge to within a very thin layer below the closest point of measurement to the plate. Rudimentary vortical flow developed slightly downstream of the leading edge, but dissipated further downstream. Although weak vortices were measured in the trailing-edge, cross-plane, these were attributed to comer separations just upstream. The turbulence activity in the streamwise corners was found to be surprisingly low, especially in the compression side of the junction. Estimates of skin-friction showed that it was lower over the majority of the trailing-edge cross-plane than in the plate boundary layer upstream of the junction. At higher incidence, flow visualisation showed that the junction region had severe stall characteristics, with 3-dimensional recirculation regions forming.

Large commercial aircraft by design typically are not capable of transporting maximum fuel capacity and maximum payload simultaneously. Maximum payload range remains less than maximum range. When an aircraft is operated on a route that may exceed its maximum payload range capability, environmental conditions can vary the payload capability by as much as 20%. An airline’s commercial department needs to know of such restrictions well in advance, to restrict booking levels accordingly. Current forecasting approaches use monthly average performance, at, typically, the 85% probability level, to determine such payload capability. Such an approach can be overly restrictive in an industry where yields are marginal, resulting in sellable seats remaining empty. The analysis of operational flight plans for a particular ultra-long routing revealed that trip fuel requirements are near exclusively predictable by the average wind component for a given route, at a correlation of over 98%. For this to hold, the route must be primarily influenced by global weather patterns rather than localised weather phenomena. To improve on the current monthly stepped approach the average wind components were modelled through a sinusoidal function, reflecting the annual repetitiveness of weather patterns. Long term changes in weather patterns were also considered. Monte Carlo simulation principles were then applied to model the variance around the mean predicted by the sinusoidal function. Monte Carlo simulation was also used to model expected payload demand. The resulting forecasting model thus combines supply with demand, allowing the risk of demand exceeding supply to be assessed on a daily basis. Payload restrictions can then be imposed accordingly, to reduce the risk of demand exceeding supply to a required risk level, if required. With payload demand varying from day of week to seasonally, restricting payload only became necessary in rare cases, except for one particular demand peak period where supply was also most restricted by adverse wind conditions. Repeated application of the forecasting model as the day of flight approaches minimises the risk of seats not sold, respectively of passengers denied boarding. / Thesis (PhD)--University of Pretoria, 2019. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautical Engineering, 1926. / Includes bibliographical references (leaves 13-14, first group). / by N.J. Medvedeff and N.N. Sinitzin. / M.S.