No description available.

No description available.

The emission of NOx from aero-gas turbine combustors, which in the present generation of designs consists mainly of thermal NOx ' is of great concern due to its potential damage to the stratospheric ozone layer. Soot production in gas turbine combustors is also undesirable since it is both the major source of exhaust smoke and, more importantly, the principal agent in thermal radiation to the combustor liner. Furthermore thermal radiation from the soot redistributes energy in the combustor, modifying the temperature field. This consequently affects the production of other pollutants, notably that of thermal NOx > since the production rate is especially sensitive to temperature. Mathematical models for predicting gas turbine combustor emissions can be divided, in general terms, into two main groups, Methods based on zonal (or modular) approach and on CFD modelling. CFD modelling allows the use of computation intensive multi-dimensional Navier-Stokes codes but cannot account for detailed chemistry which is responsible for emissions. On the other hand, although the modular approaches make significant assumptions about the mean flowfield and mixing, they employ detailed chemical kinetics. The work reported in this thesis seeks to develop a model for emission predictions in the gas turbine combustor which combines the advantage of both the modular approach and CFD modelling. The strategy was based on a pdf calculation using the Monte-Carlo simulation technique because the chemical source term is in closed form for the approach and the solution procedure requires a CFD based calculation. Averaging of the particle properties was on an extended zonal or planar basis in order to reduce computational effort. The predictions are evaluated against available experimental results and other predictions employing more conventional approaches. Since the pdf method allows the modelling of slow chemistry and simultaneous influence of multiple scalars, the thermal NO x production rate was implemented considering the effect of NO concentration itself. Predicted exit NOx concentration was higher than the measured exit level. It has been thought that this discrepancy is mainly due to neglecting radioactive heat loss for temperature calculations. The modelling of soot formation and oxidation has proved more problematic since the assumption that soot is simply perturbation to the gaseous field, analogous to the NO concentration, and temperature may be accurately described by single adiabatic flamelet are no longer valid at elevated pressure and temperature conditions. Soot bum-out is under-predicted. The computed mean soot oxidation is less than 10% of the maximum production levels, even when OH is considered to be oxidising species in addition to O2 •• Although high soot formation rate was predicted as a result of neglecting radioactive loss and using single perturbed flamelet calculation, the main uncertainties come from instantaneous soot oxidation rate and the particle size effect which influence the particle surface area.

A mobile experimental test facility has been developed to carry out the aerodynamic evaluation of hang glider wings normally performed in a wind tunnel. Longitudinal aerodynamic data obtained using this facility is presented for three modern hang glider wings, a Silhouette, Demon 175 and Magic 166, together with surface flow patterns for the latter two wings. The longitudinal stability criterion are studied and alternatives established, equivalent to the stick fixed and stick free criterion for conventional aircraft, relevant to weight shift controlled wings. These are based on the pilot's position and control force to trim. The aerodynamic data obtained from the mobile facility is used to calculate these parameters and the longitudinal static stability of each wing is examined. The influence of several rigging parameters, variable by the pilot before flight, on the longitudinal static stability and control of the hang glider are also investigated.

Increases in the price of petroleum fuels have significantly affected the importance of aerodynamic drag on commercial vehicle operating costs. The considerable savings to be made have resulted in: (i) the appearance of numerous 'add-on' devices intended to reduce the drag-of existing vehicles, and (ii) an acceptance by vehicle manufecturers of the importance of aerodynamics to their new designs. The majority of drag optimisation programmes are carried out using scale models in a wind tunnel, and the effectiveness of resulting modifications is often confined to the individual vehicle concerned. The relatively crude simulation techniques have been acceptable on the basis that potential errors are small compared to the reductions in drag that can be achieved. If the trend in reducing drag is to be maintained a greater understanding of the flow around commercial vehicle configurations will be needed, especially under simuleted,crosswind conditions, together with improvements to the wind tunnel techniques used to simulate the full scale environmen The experimental programme presented in this report is intended to Illustrate ,the influence of wind tunnel simulation technique, on the methods for reducing commercial vehicle aerodynamic-drag. result in wind tunnel tests over a 'range of simulated crosswind conditions and levels of free stream turbulence are present illustrate the significance of variations in Reynolds number, vehicle geometry, and wind tunnel size on the pressure distribution 2. and resulting diagonal forces on the vehicle. I.Jrfece pressure contours are ceteidgued.t0 give insight into the flowfield, around the vehicle in relation to the problems of body fouling and water spray generation although analysis here specifically concerns aerodynamic drag. Techniques for reducing drag relate primarily to modifications Of the forebody flowfield and results from a number of experimental Programmes are collated to illustrate the effectiveness of various techniques on different vehicle geometries.

Model updating is an important issue in engineering. In fact a well-correlated model provides for accurate evaluation of the structure loads and responses. The main objectives of the study were to exploit available optimisation programs to create an error localisation and updating procedure of nite element models that minimises the "error" between experimental and analytical modal data, addressing in particular the updating of large scale nite element models with severe requirements on the mode shapes correlation. A new methodology and procedure that allows the semi-automatic adjustment of a large nite element dynamic model of a structure to better represent the dynamic characteristics of an actual structure was developed. The key aspect of the procedure is a "two steps" optimisation process to achieve a complete correlation of the modal data. Eigenfrequency deviations and mode shapes cross-othogonality (CO) and/or modal assurance criterion (MAC) are used in the objective functions for the estimation problem of the updating parameters, that are the variables for tuning the analytical model. Theoretical aspects and practical implementation conceming CO and MAC, and their derivatives, have been fully developed and the advantages of using these mode correlation indices in the objective function have been largely commented. The selection of the updating parameters is a complex issue and can be still considered a partially open point. In the new procedure the suggested automated selection of the updating parameters by means of a preliminary calculation of the element modal strain energy and eigenvalue sensitivities is adequate for the reduction of the frequency deviations but could not be to improve the correlation indices of the mode shapes. The new procedure was successfully applied four times: to a cantilever beam model, the Garteur model, the Spacehab dynamic model and the Mini-Pressurised Logistics Module model. The last application was a real life application on a large scale structural mathematical model and in this case the procedure was mainly used for error localisation purposes. The developed procedure is robust, effective and efficient, thus the original objectives of the study were largely met.

No description available.

No description available.

The unique University of Durham transient cross-wind facility has been developed such that sharp edged, finite length, cross-wind gusts with a relative yaw angle of 22' can be developed at the rate of 1000/hr. This cross-wind facility uses the transient interaction of two wind tunnel jets to create these gusts, with the fully automated, rapid, repeatable gust production process allowing ensemble averaging to significantly improve data quality. The cross-wind gust characteristic, as observed for the empty working section, has some inherent problems. A yaw angle undershoot, and more importantly, an overshoot occur at the leading edge of the gust. A transient total pressure overshoot is also observed at the leading edge of the gust. Computational fluid dynamics (CFD) simulations of the empty working section have replicated these anomalies, and suggestions are proposed for their elimination. Two aerodynamic models were tested in this facility, each being subjected to transient cross-wind gusts of 10 model lengths. Both models exhibited significant transient force and moment overshoots. These overshoots were found to be a consequence of delayed pressure development in regions of separated flow, with full flow development requiring up to seven model lengths of cross-wind gust. These results, which cannot be replicated by any steady testing procedure, confirm the requirement for transient testing, if transient forces and moments are required.

An oblique shock generated by a variable-angle wedge on the side wall of a wind tunnel, has been used to investigate the three-dimensional glancing interaction problem. The shock interacts with the turbulent boundary layer growing along the side wall. Two related test programmes have been completed using a 2.5 x 2.5 inch intermittent tunnel and a 9 x 9 inch continuous-running tunnel. For both the test programmes, the Mach number was approximately 2.5 and the Reynolds number relative to the wall boundary-layer thickness 5 x 10 4 . The experimental results include oil-flow pictures, vapour-screen and smoke photographs,wall pressure distributions, local heat transfers, wall surface temperatures and viscous layer surveys. The experimental results suggest that the interaction reg10n consists of two different viscous layers between which an ordinary separation can take place, (the double viscous layer flow-field model). The three- dimensional separation is found to depend significantly on the pressure rise in the direction normal to the swept shock. In this sense the separation is similar to the two-dimensional case.