No description available.

No description available.

Blade vibrational amplitude in aero-engines bladed discs can be significantly amplified due to the uneven distribution of blade mechanical properties from the uncertain sources in manufacturing process, assembly tolerances and operational wear and tear. The possibly ensuing higher vibrational level on the blades is regarded as one of leading causes for the shortened high cycle fatigue life of a whole bladed disc system. This mistuning problem therefore has attracted tremendous attentions from aero-engine industries and research communities since 1960s. One of the key aspects of mistuning is how to quantify efficiently the effect of those uncertainties on the maximum blade dynamic response in a bladed disc. However, in spite of a great deal of research efforts poured into this topic, the mistuning problem is still considered a challenge from the design perspective, because of the unacceptable computational costs associated with the related dynamic analysis, even when using state-of-the-art reduced order models. The computational costs would be further increased when physical aspects like the non-linearity from the large geometry deformation of blades, contact friction in the dovetails and aerodynamic couplings are taken into account. The complexity of the simulation problem associated to mistuning increases when reliability analysis is also required. The main achievements of the present study . consist in the development of deterministic and probabilistic based reduced ordvr techniques to enhance the computational efficiency for linear . mistuning analysis of bladed disc systems. A novel parametric reduced order model using a simplified structural layout is presented to represent the equivalent dynamic behavior of a typical aero-engine blade. A comparative case study is then carried out to investigate the application of using this novel beam frame assembly to increase the computational efficiency for mistuning analysis of a whole bladed disc system. The results obtained from the beam frame assembly is benchmarked by three state-of-the-art finite element based reduced order models. After that, this study looks into the application of novel stochastic techniques for the reliability analysis of mistuned bladed discs in order to reduce the number of samples required by classical Monte Carlo Simulations. The feasibility of using subset simulation techniques is assessed for probabilistic analysis of a mistuned bladed disc system. The work finally investigates the efficient matrix inversion techniques to increase the ~omputational efficiency of stochastic analysis of bladed discs. Two classical matrix inversion techniques, namely Neumann expansion techniques and Sh~rman Morrison formula, are assessed respectively. Based on the results of the assessment, a more robust inversion technique based on Neumann expansion method and matrix factorization techniques is proposed and validated through two case studies.

No description available.

No description available.

No description available.

No description available.

The reduction of NOx, soot and other emissions in aero or industrial gas turbines are engage by the concept of new combustion system such as the lean premixed pre-vaporized system. Which brings with it several engineering solutions such as combustion instabilities, flashback and autoignition. An experimental test rig named Sheffield Rapid Compression Machine (Shef-RCM) is designed to investigate the autoignition chemistry of alternative fuels relevant to gas turbine plant and to handle high boiling point long chain hydrocarbon fuels. The Shef-RCM incorporates a hydraulic stopping mechanism, piston release mechanism, an optimal crevice piston design and a reactor chamber is designed which utilises the direct test chamber method for easy admittance of fuels. The machine is pneumatically driven and hydraulically stopped. The novelty in the design of the Shef-RCM is the introduction of a piston release mechanism (brake) pneumatically operated use to hold the reactor piston in position at its bottom dead centre. A computational fluid dynamics study on crevice piston was undertaken to produce the best-optimized crevice piston head design that will suppress the roll-up vortex to enhances the homogeneity of the temperature field of the reactor chamber. The simulation used a 2-Dimensional computational moving mesh axisymmetric in the commercial code of Ansys fluent. The model adopted for this calculation was the laminar flow. Appropriate choice of the model parameter was taken into consideration during the simulation to reduce errors caused by a poor mesh quality. These parametric studies examine the time step size and the mesh density, which was been deemed necessary for running the simulation to handle errors of negative cell volume. The parameters maintained for the model are a constant stroke length of 142 mm with a volume clearance height of 17 mm. Further optimisation of a 282 mm3 crevice volume on the width resulted to five different crevice widths of 3 mm, 5 mm, 7mm, 9 mm and 12 mm respectively. The widths of the piston head crevice of 5mm gave a better result regarding the peak pressure profile and maintained a homogeneous temperature field at the end of the TDC at post compression time of about 40ms. Performance characterization of the Shef-RCM, using inert gases, N-Heptane and Jet A-1 showed that the experimental data obtained was highly reproducible and repeatable. The machine is vibration free, allows for fast compression, less than 35 ms, an obtainable compressed gas pressure of 22 bar. The estimation of the compressed gas temperature at the top dead centre using numerical modelling was 698 K; the heat loss implemented in the model used an effective volume approach, which showed a perfect match for the model with experiment. Ignition delay time measurement for Jet A-1 are reported for low to intermediate temperatures regime (734 ≤ TC ≥ 815)K, compressed gas pressure, PC = 6 and 10 bar and equivalent ratios, ф= 0.5, 0.75 and 1.0 in air. Jet A-1 exhibited Arrhenius behaviour at 6 bar and 10 bar except for some suspected traces of NTC at ф = 0.5,which needed to be fully established. No evident of Negative Temperature Coefficients (NTC) behaviour at a higher pressure of 10 bar. The kinetic modelling conducted for Jet A-1 used Ranzi et al.[1] model with Dooley et al. [2] and Aachen[3] surrogate mixture. At a compressed pressure of 6 bar, ф= 0.75, the model predicted a shorter ignition delay time and displayed a two stage ignition delay time for Jet A-1 fuel, and the model was in agreement with the experiment. The Shef-RCM facility has also been used to measure the combustion behaviour of Banner-Solvent at low to intermediate temperature regime (718 ≤ TC ≥ 916) K at compressed pressure, PC = of 6 and 10 bar, and equivalence ratios, ф= 0.5, 0.75 and 1.0 in air. Various diluent mixtures were carried out to alter the end gas temperature, it was found that ignition delay within the temperature range of 718 – 916 K exhibited NTC behaviour at lean condition and stoichiometric. Banner-Solvent reacts faster compare to Jet A-1, and this showed some trend of Negative Temperature Coefficient behaviour at a compressed gas pressure of 6 bar. Experimental measurement of the ignition delay response of UCO-HEFA at low to intermediate temperature regime (680 ≤ TC ≥ 777) K at compressed gas pressure, PC = 6 and 10 bar, and equivalence ratios, ф= 0.5, 0.75 and 1.0 in air was studied. The effects of temperature, pressure, and equivalence ratio and oxygen concentration on the ignition delay time was investigated. The overall reactivity of the three fuels showed that Banner-Solvent had showed a higher reactivity than Jet A-1 and UCO-HEFA at 10 bar compressed gas pressure. At 6 bar compressed gas pressure, UCO-HEFA showed some signs of NTC behaviour. The uncertainty for the three fuels was considered and this was seen to be within the limits compared in literature. The global correlation for Jet A-1 and UCO-HEFA were derived for both fuels.

The investigation presented attempts to develop a suitable mathematical model which may be relied upon to predict the air motion within the cylinder of a motored, four-stroke direct-injection diesel engine. Using a method of hot wire anemometry, a three-wire anemometer was developed for measuring the magnitude and direction of the three-dimensional velocity vector within a variable density flow similar to that encountered inside a motored engine cylinder and an exhaustive experimental program undertaken to justify the technique. The results of the experimental program showed that the magnitude of, the. Three-dimensional velocity vector may be measured within an accuracy of ± 9% whilst the direction may be determined within ± 12%. Applying the method to an engine cylinder, measurements of the air motion were recorded over a range of engine speeds (500-1500 rpm) and the effect of a masked inlet valve and supercharging the engine at 10 psig were also investigated.

The investigation described in this thesis is a study of instantaneous heat fluxes (total and radiative) and their variation with operating conditions in a high-swirl direct-injection diesel engine. The problem is approached experimentally and methods for prediction of convective and radiative components are suggested. Total heat fluxes were measured using a thin-film type thermocouple developed in the course of the work, while the radiant flux was measured by a pyroelectric infrared detector. The experimental observations demonstrate variations in local heat fluxes which are moderate under motored conditions but large in the fired engine. Some of the observed features of flux variation with time and with location have been shown to be qualitatively explicable in terms of probable local events during the cycle.