John Allport

Layer manufactured production tooling incorporating conformal heating channels for transfer moulding of elastomer compounds

Abstract This paper reports the results of a study designed to assess the extent to which layer manufacturing processes were able to produce production quality tools for transfer moulding of elastomer compounds. The specific layer manufacture process considered was the DTM RapidSteel process. Tools produced using this process were used in industrial trials to assess productivity benefits arising from the use of conformal heating channels. Thermocouple gauging of the tools was used to assess the effectiveness of both conventional electrical platen heating and the conformal channel heating. It is concluded that conformally heated RapidSteel tools offer significnt productivity and process repeatability benefits when compared to conventional tooling for transfer moulding of elastomer compound. Cost modelling of the moulding process indicates that these productivity benefits translate to significantly reduced life cycle costs for the manufacture of all but the smallest batch sizes.

Statistical Mechanics Material Model for the Constitutive Modelling of Elastomeric Compounds

Material models for the finite element analysis (FEA) of polymeric and elastomeric compounds are only available in limited form in most commercial finite element (FE) packages. The most common are the phenomenological Mooney-Rivlin and the Ogden models, for which the constants bear no relationship to the physical or chemical characteristics of the rubber and their derivation is difficult. Both models are limited in their accuracy for filled rubbers used in combined states of tensile and compressive deformation, and since these are common operational conditions for engineering components such as drive couplings, engine mounts and torsional vibration dampers, their use in engineering analyses is restricted. In this paper a statistical mechanics material modelling approach for synthetic, filled elastomeric compounds in FEA is presented. Using styrene-butadiene rubber (SBR) as an example, the theory and its application in the commercially available ABAQUS finite element analysis program is explained. FE models of tensile and compressive specimens in two and three dimensions are used to demonstrate the use of the model, and results are presented, discussed and compared with measured data. Good correlation in both tension and compression is demonstrated. A practical application of the model to the SBR blocks in a Holset torsional drive coupling is presented; this analysis involves complex issues of mesh design and contact modelling. The results show good agreement with measured performance, and clearly demonstrate how this type of material modelling approach can be effectively used in the computer aided engineering and design of engineering rubber components.

Dynamics of mistuned radial turbine wheels

This paper presents investigations carried out at Holset into the dynamics of mistuned radial turbine wheels, including a literature review, a lumped parameter model, identification of the most responsive blade, distribution of the peak maximum order response and a method of mistiming identification.

Increasing Compressor Wheel Fatigue Life Through Residual Stress Generation

Cast aluminium compressor wheels in turbochargers may fail following cyclic loading in service due to crack growth from the highly stressed bore of the wheel. In this paper it is proposed to subject wheels to a single over-speed event to generate beneficial, compressive residual stresses at the bore of the wheel and hence reduce stresses at the working speeds. A theoretical model has been identified to simulate this process and a technique developed to determine the model input parameters. This closed form analytical model shows good correlation with a detailed finite element analysis over a wide range of over-speed events.

Integrated electrical machine-turbo machinery

Global warming and climate change due to rising levels of greenhouse gases have placed significant pressure on the automobile industry to adopt more clean fuel, transportation electrification, and waste energy recovery technologies. As a result, several electrically assisted or driven turbo-machines have been proposed such as turbochargers, turbo-compressors, and electrical boosters. Therefore, the electrification of turbo-machinery has been trending for the past decade. All the systems mentioned above consist of a conventional electrical machine connected to the turbo-machinery by a shaft, making the system relatively large, heavy, costly and mechanically complex. In this paper, an integrated electrical machine-turbo machinery concept is proposed. It consists of an electrical machine mounted around a salient rotor that is shaped like an axial flow turbo-machinery wheel. The electrical machine can be used as a motor to drive or assist the operation of the turbo-machine or it can operate as a generator powered by the gas or fluid flow. Compared to the conventional electrically derived or assisted turbo-machine systems, the proposed system is expected to decrease the overall size, weight and complexity. In order to illustrate this concept, an initial multi-physics feasibility study is presented. Electromagnetic and mechanical, performance are calculated and investigated using FEA. Additionally, aerodynamic consideration has been illustrated.

Ported shroud flow processes and their effect on turbocharger compressor operation

The ported shroud (PS) self-recirculating casing treatment is widely used to delay the onset of the surge by enhancing the aerodynamic stability of the turbocharger compressor. The increase in the stable operation region of the turbocharger compressor is achieved by recirculating the low momentum fluid that blocks the blade passage to the compressor inlet through a ported shroud cavity. While the ported shroud design delays surge, it comes with a small penalty in efficiency. This work presents an investigation of the flow processes associated with a ported shroud compressor and quantifies the effect of these flow mechanisms on the compressor operation. The full compressor stage is numerically modelled using a Reynolds Averaged Navier-Stokes (RANS) approach employing the shear stress transport (SST) turbulence model for steady state simulations at the design and near surge conditions. The wheel rotation is modelled using a multiple reference frame (MRF) approach. The results show that the flow exits the PS cavity at the near surge condition in the form of three jet-like structures of varying velocity amplitudes. Net entropy generation in the compressor model is used to assess the influence of the ported shroud design on the compressor losses, and the results indicate a small Inlet-PS mixing region is the primary source of entropy generation in the near surge conditions. The analysis also explores the trends of entropy generation at the design and the near surge condition across the different speed lines. The results show that the primary source of entropy generation is the impeller region for the design condition and the inlet-PS cavity region for the near surge condition.

Analysis of a tilted turbine housing volute design under pulsating inlet conditions

Radial inflow turbines are widely used in the automotive turbocharger industry due to the greater amount of work that can be extracted per stage and their ease of manufacture compared with equivalent axial designs [1]. The current industry trend towards downsized engines for lower emissions has driven research to focus on improving turbine technologies for greater aero-thermal efficiency. Consequently, mixed flow turbines have recently received significant interest due to a number of potential performance benefits over their radial counterparts, including reduced inertia and improved performance at low velocity ratios. This paper investigates the performance of a tilted volute design compared with that of a radial design, under steady state and pulsating flow conditions. The tilted volute design was introduced in an attempt to improve inlet flow conditions of a mixed flow turbine wheel and hence improve performance. The investigation is entirely computational and the approach used was carefully validated against gas stand test results. The results of the study show that under steady state conditions the tilted volute design resulted in stage efficiency improvements of up to 1.64%. Under pulsating flow conditions, the tilted housing design resulted in a reduction in incidence angle and a maximum cycle averaged rotor efficiency improvement of 1.49% while the stage efficiencies resulted in a 1.23% increase. To assess the loss mechanisms within the rotor, the entropy flux generation through the blade passage was calculated. The tilted housing design resulted in reductions in leading edge suction and shroud surface separation resulting in the improved efficiency as observed.