Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

The numerical simulation of flow and heat transfer over turbine blades involving laminar-turbulent transition is presented. The predicted results are compared with the experimental surface heat transfer and pressure distributions for two transonic turbine blades over a wide range of flow conditions. The time-dependent, mass-averaged Navier-Stokes equations are solved by an explicit four-stage Runge-Kutta scheme in the finite volume formulation. Local time stepping, variable-coefficient implicit residual smoothing and a full multigrid method have been implemented to accelerate the steady state calculation. The turbulence is simulated by the algebraic Baldwin-Lomax model together with an explicitly imposed model for transition. For comparison, the low-Reynolds-number version of the two-equation (k-∊) model of Chien is also used. The modified Baldwin-Lomax model performs well in predicting the onset of laminar-turbulent transition, whereas the Chien model shows a tendency to mimic the transition early and over a shorter distance.

This paper presents the results of numerical prediction of the lubricant film thickness and pressure distribution in concentrated counterformal point contact under isothermal conditions. The operating conditions, which include load and speed of entraining motion, promote the formation of ultra-thin films; these are formed under the combined action of elastohydrodynamic lubrication (EHL), the surface contact force of solvation and molecular interactions due to the presence of Van der Waals forces. A numerical solution has been carried out, using the low-relaxation Newton-Raphson iteration technique, applied to the convergence of the hydrodynamic pressure. The paper shows that the effect of surface forces become significant as the elastic film (i.e. the gap) is reduced to a few nanometres. The numerical predictions have been shown to conform well to the numerical work and experimental findings of other research workers.

The two-dimensional pressure control valve is a piloted control valve which functions by using both linear and rotary motions of a single spool. A groove on the spool land, incorporating a sensing channel, forms the pilot stage to control the pressure of a spool chamber, while the load pressure is fed to the other spool chamber. To sustain the balance of the force across the spool, the load pressure must follow the change of pressure variation along the groove while the spool is in rotary motion. The geometric parameters of the groove and the spool-to-sleeve clearance have significant effects on both the static and dynamic characteristics of the valve. Increasing the sectional size of the groove results in a large Reynolds number and the static property of the valve thus changes from that of linearity owing to the entrance effect. The linearity of the static property is also affected by the leakage through the spool-to-sleeve clearance. The dynamic characteristics of the valve are dependent upon both the structural parameters and the tune constant of the load. The stability and dynamic response were investigated under different structural parameters and time constants of the load using both linear theory and simulation methods. Experiments were designed to obtain the static and dynamic characteristics of the valve and the leakage through the pilot. A balance should be made between the linearity of the static property and the response speed; it was found that both fairly linear static and desired dynamic characteristics could be simultaneously maintained for the two-dimensional pressure control valve.

The three-colour method has been developed in order to turn chromatic information in charge coupled device (CCD) camera images of combustion into flame temperature and soot concentration measurements. The method showed the following advantages over the two-colour method from which it is derived: only one camera is needed; no further calibration is required once the response curve of the camera is known; it does not rely on light intensity but on ratios between colour components, making it easy to adapt to different operating points with different name brightness. The results on temperature evaluation were compared with a thermodynamic model, and better agreement was found in the late stages of the cycle, when the radiation from chemical reactions becomes negligible. The error analysis showed that the calculations for soot concentration are ill-conditioned, but when the results are integrated to give a soot loading the accuracy is improved and there is clear evidence of soot evolution and destruction during combustion.

A quick and easy but comprehensive identification method for rotating asymmetry in rotating machines is proposed, based on the complex modal testing method. In this work it is shown that the reverse directional frequency response function (reverse dFRF), which indicates the degree of asymmetry, can be identified with a simple testing method requiring only a single vibration sensor and a single exciter. To clarify physical realization associated with estimation of the reverse dFRF, its relation to the conventional frequency response functions, which are defined by the real input (excitation) and output (vibration measurement), are discussed extensively.

Artificial neural networks (ANNs) have been used to detect faults in rotating machinery for a number of years, using statistical estimates of the vibration signal as input features, and they have been shown to be highly successful in this type of application. Support vector machines (SVMs) are a more recent development, and little use has been made of them in the condition monitoring (CM) arena. The availability of a limited amount of training data creates some problems for the use of SVMs, and a strategy is offered that improves the generalization performance significantly in cases where only limited training data are available. This paper examines the performance of both types of classifier in one given scenario—a multiclass fault characterization example.

The Weibull three-parameter model is widely used in the analysis of reliability data, since it provides a good fit to many, but not all, data cases. In this work an analysis is presented in which locally constant hazard rate functions are applied in the analysis. By defining concomitant fuzzy reliability functions as overlapping fuzzy sets, the limited ranges may be conjoined to provide an extensive continuous reliability function. The efficacy of this treatment is tested with three different typical cases of published physical data that were previously the subjects of Weibull graphical analysis. It is found that in each case the treatment is effective. Different phases of the failure pattern of each case are identified and characterized by ‘time’ constants. The treatment is not limited to three parameters, as in the Weibull case, and it is therefore more flexible. It provides a deeper insight into the underlying failure mechanisms and may be expected to provide a wider range of applications, both within reliability data analysis and in other fields, and can form part of a knowledge-based system.

Centrifugal impellers are exposed to downstream circumferential outlet distortions due to non-axisymmetric volutes or diffusers. This paper explores the effect of circumferential outlet distortion on the flow characteristics at the impeller exit of a centrifugal pump. A fence with non-uniform height was installed at the vaneless diffuser exit to create the outlet distortion, and then unsteady velocity and static pressure were measured at the impeller exit. The instantaneous and mean flow fields at the impeller exit varied with the circumferential position. Plots of the flows against the local flowrate showed hysteretic loops that deviated from the quasi-steady curves obtained from the flows without the fence. When the assumption of quasi-steady variation was applied to the present impeller-diffuser interaction, the prediction for the total and static pressure was reasonable but showed a phase difference for the absolute velocity.

A comprehensive study of the effects of acceleration and braking on motorcycle stability is presented. This work is based on a modified version of a dynamic model presented earlier, and is thought to be the most comprehensive motorcycle dynamic model in the public domain. Extensive use is made of both non-linear and linearized models. The models are written in LISP and make use of the multibody modelling package AUTOSIM. There is novelty in the way in which control systems have been used to control the motorcycle drive and braking systems in order that the machine maintains desired rates of acceleration and deceleration.

The results show that the wobble mode of a motorcycle is significantly destabilized when the machine is descending an incline or braking on a level surface. Conversely, the damping of the wobble mode is substantially increased when the machine is ascending an incline at constant speed, or accelerating on a level surface. This probably accounts for the pleasingly stable ‘feel’ of the machine under firm acceleration.

Except at very low speeds, inclines, acceleration and deceleration appear to have little effect on the damping or frequency of the weave mode. Non-linear simulations have quantified the known difficulties to do with rear tyre adhesion in heavy braking situations that are dominated by rear wheel braking.

The air-side performance of three new slit fin-and-tube heat exchangers under dehumidifying conditions is reported. The effects of the number of rows of tubes, the fin pitch and the inlet relative humidity on air-side performance are reported. It is found that for type I slits, which are characterized by a small louvre angle (convex-louvre configuration), the test results show that the sensible heat transfer performances are relatively independent of fin pitch. However, for type III slits, which feature the smallest distance between adjacent slits, a drop of heat transfer performance for N= 1 and F _p = 1.81 mm is observed. It is very likely that this phenomenon is related to the ‘non-recovery wake effect’ caused by the slit geometry. A correlation is proposed for the slit fin configuration; the mean deviations of the proposed heat transfer and friction correlation are 8.0 and 8.1 per cent respectively.

Non-equilibrium energy transport takes place in solids once the laser pulse duration reduces to picoseconds or less. It is this energy transfer mechanism that defines the laser interaction process and therefore the rate at which the material is heated through the collisional process. In the present study, laser short-pulse heating of a gold surface is considered. An electron kinetic theory approach is introduced to model the energy transport process in three dimensions. The governing equation of energy transport is solved numerically, and the electron and lattice site temperatures are predicted. In order to validate the electron kinetic theory predictions, a two-equation model is employed to compute the temperature field in the substrate material. It is found that energy transport due to the diffusional process is unlikely during the heating period considered at present. The predictions of electron kinetic theory agree well with the results obtained from the two-equation model.

Using an energy technique, the classical solution for the static formulation of the tangential follower problem is reproduced considering the more general case of a column with variable stiffness. The method of solution allows for a more delicate analysis of the phenomena associated with this problem. It is shown that the classical problem is, in a sense, overdetermined. The problem is then reformulated to permit the existence of critical loads for the static case.