Analysis of a Virtual Prototype First-Stage Rotor Blade Using Integrated Computer-Based Design Tools

The present paper outlines a practical methodology for improved virtual prototyping, using as an example, the recently re-engineered, internally-cooled 1st stage blade of a 40 MW industrial gas turbine. Using the full 3-D CAD model of the blade, a CFD simulation that includes the hot gas flow around the blade, conjugate heat transfer from the fluid to the solid at the blade surface, heat conduction through the solid, and the coolant flow in the plenum is performed. The pressure losses through and heat transfer to the cooling channels inside the airfoil are captured with a 1-D code and the 1-D results are linked to the three-dimensional CFD analysis. The resultant three-dimensional temperature distribution through the blade provides the required thermal loading for the subsequent structural finite element analysis. The results of this analysis include the thermo-mechanical stress distribution, which is the basis for blade life assessment.

Conjugated Heat Transfer in Skirt Hot Box in Pressure Vessels

Pressure vessels are common equipment in oil, gas and petrochemical industries. In a hot containing fluid vessel, excessive temperature gradient at junction of skirt to head (weld line), can cause unpredicted high thermal stresses; Thereby fracture of the vessel may occur as a result of cyclic operation. Providing a hot box (air pocket) in crotch space is a economical, applicable and easy mounted method in order to reduce the intensity of thermal stresses. Natural convection due to temperature difference between the wall of pocket, will absorb heat near the hot wall (head of the vessel) and release that near the cold wall (skirt of the vessel), then the skirt wall conducts heat to the earth as a fin. This conjugated heat transfer removes the temperature gradient boundary at welded junction. This phenomena will lead the temperature gradient on the weld line from a sudden to smooth behavior, thereby the skirt-head junction, that is a critical region, could be protected from excessive thermal stresses. In this paper the profit of hot box and conjugated heat transfer in cavity has been demonstrated experimentally. As a result it is shown that the conductive heat transfer through the skirt (which acts as a fin) ensures the continuation of natural convection in the box. Also the governing equations has been solved numerically and compared with experimental results.

Near Optimal Grinding Process Design Using Neural Network and Real Coded Genetic Algorithm

A typical grinding process is an essential manufacturing operation and has been considered to be a precise and economical means of shaping the parts into the final products with required surface finish and high dimensional accuracy. The need to economically process hard and tough materials which can withstand varying stress conditions to ensure prolonged service life of parts has become a real challenge for researchers and practitioners. In this context, with the advance development and automation of grinding processes, use of appropriate modelling and optimization techniques has been continually emphasized. In view different types of end product and process requirements in grinding processes, optimization often becomes non-linear, multiple response constrained problem with multi-modal distribution of response quality characteristics. The objective of this study is to apply back propagation neural network modelling technique for prediction of a computer numeric-controlled (CNC) rough grinding process behaviour, and thereby determine overall near optimal process design using real coded genetic algorithm. The study proposes an integrated approach using back propagation neural network algorithm, composite desirability function, and real-coded genetic algorithm. The effectiveness and suitability of the approach is determined based on data analysis of a single-pass 6-cylinder engine liner CNC rough grinding (honing) operation in a leading automotive manufacturing unit in India.

On the Use of Fast-Response Pressure Transducers in a Common-Rail Diesel Injection System

The aim of this paper is to investigate the use of fast-response pressure transducers for measuring the instantaneous pressure in different sections of a common-rail diesel injection system, both for a single injection and for multiple injections. The influence of the pressure transducer onto the measured pressure is evaluated numerically by comparing the pressure history computed without the pressure transducer and that computed with the presence, and thus with the disturbance, of this sensor. A new electric circuit is proposed in substitution of the standard electronic central unit, which allows to modify the injection parameters and to perform injections on a test rig, as done in the automotive applications. Experimental results are provided both for a single injection and for multiple injections, to demonstrate the capabilities of the proposed test bench for the unijet injectors.

Synergy-Based Approach to Bad Engineering

In the present paper unique data about initial shortcomings in the design and application of different industrial and consumer products are presented. The research area covers all of the products’ development stages beginning with factory automation and equipment control systems, and continuing with the design and realization of light fittings up to follow-up on the product development of office machines. The statistical results of this research are presented. Further the essence of the synergy-based approach to the design process, focussing on the most common human faults/mistakes, is clarified. Evidence is presented to show that the reason for human shortcomings is either the lack of synergy in teamworking or problems in inner personal communication. A detailed definition of the concepts of positive and negative synergy, with examples from both categories is given. Guidelines are given to reduce human risks at the conception of interdisciplinary systems design to avoid bad engineering. A framework for the synergy-based design of interdisciplinary systems is presented capable of adapting to the competences of the design team.

Washers to Reduce Vibration and Noise From the Injection Molding Process

The noise and vibration problems created by injection molding machines can be moderated by the installation of absorbers. The pull rods of the machine, which are guided to the molding movements, might be a better location for mounting a spring, rubber or hybrid elastomer for energy absorption and reduction of noise and vibration. In this paper, some special washers are designed to fit the guide rods and performance tests are carried out. The results show that noise and vibration decreased over 10 dB and 2 times, respectively.

Thermomechanical Model and Experimental Analysis of Progressive Fatigue Damage in Steel Specimens

This paper presents a thermomechanical model to predict the surface temperature evolution of a specimen during a fatigue test. In particular, the aim of this theoretical approach is to evaluate the amount of accumulated fatigue damage in the material, on the basis of its temperature growth indicated as damage parameter. To do that, a thermomechanical model has been developed and applied to a unidimensional steel specimen, with rectangular cross-section, fatigued by alternate axial stresses. Temperature variation along the thickness of the specimen has been disregarded. Thermomechanical differential equation has been integrated by applying both initial and boundary conditions. Temperature evolution of steel specimens measured during fatigue tests by means of thermographic techniques has been compared to the corresponding predicted by the theoretical model.

Enhanced Splash Models for High Pressure Diesel Sprays

Mixture preparation is a crucial aspect for the correct operation of modern DI Diesel engines as it greatly influences and alters the combustion process and therefore, the exhaust emissions. The complete comprehension of the spray impingement phenomenon is a quite complete task and to completely exploit the phenomenon a mixed numerical-experimental approach has to be considered. On the modeling side, several studies can be found in the scientific literature but only in the last years complete multidimensional modeling has been developed and applied to engine simulations. Among the models available in literature, in this paper, the models by Bai and Gosman [1] and by Lee et al. [2, 3] have been selected and implemented in the KIVA-3V code. On the experimental side, the behavior of a Diesel impinging spray emerging from a common rail injection system (injection pressures of 80 MPa and 120 MPa) has been analysed. The impinging spray has been lightened by a pulsed laser sheet generated from the second harmonic of a Nd-YAG laser. The images have been acquired by a CCD camera at different times from the start of injection (SOI). Digital image processing software has enabled to extract the characteristic parameters of the impinging spray with respect to different operating conditions. The comparison of numerical and experimental data shows that both models should be modified in order to allow a proper simulation of the splash phenomena in modern Diesel engines. Then the numerical data in terms of radial growth, height and shape of the splash cloud, as predicted by modified versions of the models are compared to the experimental ones. Differences among the models are highlighted and discussed.

Prediction of Residual Stresses and Buckling Distortion in Welding of a Thin Wall Aluminum Butt Joint

In this paper, global welding buckling distortion of a thin wall aluminum butt joint is investigated. To determine longitudinal residual stresses, a thermo-elastoplastic model is employed; analysis of thermal model and elastic-viscoplastic (Anand) model are decoupled. By using birth and death element method and time dependent model, molten puddle motion (speed of welding) is modeled. Three dimensional nonlinear-transient heat flow analysis has been used to obtain temperature distribution. By applying thermal results and using three dimensional Anand elastic-viscoplastic model, stress and deformation distributions are obtained. Residual stresses are applied on a structural model and by using eigenvalue methods, global buckling instability of butt welded joint is determined. The result of buckling investigation in the numerical model is compared with the result of an experiment.

Mathematical Modelling of Particle Formation in Combustion Processes

In recent years the problem of studying particle formation and evolution in turbulent flames has become increasingly important, for both environmental and technological reasons. Information on particle size and morphology is often required, since these characteristics largely influence the effects of particulate matter on human health and global climate in the case of soot. A mathematical model able to describe the evolution of these particulate systems must solve the population balance equation within a Computational Fluid Dynamics (CFD) code that predicts the temperature, composition and velocity fields of the flame. In this work, the recently proposed Direct Quadrature Method of Moments (DQMOM) is applied to the study of soot formation in turbulent non-premixed flames. The model takes into account nucleation, molecular growth, oxidation and aggregation of soot particles; simplified kinetic rates are employed, while velocity and scalar fields are computed by simulations based on the solution of the Reynolds Averaged Navier Stokes (RANS) equations. Different population balance formulations are implemented and compared and results show that DQMOM is a suitable modelling tool; comparison of predictions with experimental data shows that the model accurately describes the morphological properties of soot aggregates.