Study of aero-engine oil-air separators

For aero-engines, oil-air separation is a key function, and one approach to assessing separator effectiveness is computational fluid dynamics (CFD). The two-phase flow is complex and oil can be present in different forms (for example, droplets, mist, film). However, necessary modelling simplifications may affect solution accuracy and range of validity. This article presents a modelling methodology for oil-air separators; the effect of simplifications is discussed and their relative magnitude assessed. Comparison with available experimental data is presented. It is concluded that although simplification has an impact, the significant features of the oil-air separator are predicted with sufficient accuracy to allow design comparisons. Two separator configurations, one internal to a bearing chamber and one external, are modelled and the data presented. Flow fields are compared and the effectiveness of the separators in removing oil droplets prior to impact on the breather (primary separation) presented. The separation performance of the external design is largely independent of shaft speed, with all droplets >3 μm removed before impact on the breather. The critical droplet diameter of the internal design is larger, varying with breather configuration and shaft speed but the power loss is an order of magnitude lower than for the external design

Noise levels and noise perception from small and micro wind turbines

Noise concerns frequently pose a barrier to widespread implementation of wind turbines and while the perception of noise from large turbines has been investigated, there is a relative gap in the research for small and micro wind turbines. This paper presents findings from interdisciplinary research linking noise measurements from small wind installations with an investigation into the effect of individual personality traits and noise perception. A survey distributed to households living close to one of 12 micro or small turbine sites, coupled with environmental noise measurements was analysed. The survey showed that the most commonly perceived noises are ‘swooshing’ and ‘humming’, the presence of which may be inferred from the measured frequency spectra. Exploration of survey results showed individuals with a more negative attitude to wind turbines perceive more noise from a turbine located close to their dwelling and those perceiving more noise report increased levels of general symptoms. Individuals' personality also affected attitudes to wind turbines, noise perception from small and micro turbines and symptom reporting

A CFD and experimental investigation into a non-intrusive method for measuring cooling air mass flow rate through a synchronous generator

This paper presents a detailed methodology for a non-intrusive measurement of cooling air mass flow rate that enables an overall machine evaluation. This approach enables the simultaneous measurement of air mass flow with shaft torque at differing operating points, while minimising the change in air flow introduced by the measurement system. The impact of geometric parameters in the designed system are investigated using a detailed 180° CFD model. Special attention was paid to minimising their influence on pressure drop, mass flow rate through the machine and measurement uncertainty. Based on the results of this investigation, the system was designed and manufactured and the experimentally measured data was used to validate the CFD predictions. For the as optimal identified configuration, the flow rate is predicted to decrease by 2.2 % relative to unrestricted operation. The achieved measurement uncertainty is ±2.6 % at synchronous speed

An investigation into the use of CFD to model the co-firing of Jatropha curcas seed cake with coal

Jatropha curcas seed cake is a potential candidate for co-firing with coal. Combustion modelling using Ansys Fluent 14.0 was carried out to assess the combustion and co-firing characteristics of untorrefied and torrefied Jatropha curcas seed cake. The effect of torrefaction on the devolatilisation characteristics, flame properties and consequently NOx pollutant formation was established. Compared to the torrefied biomass, the untorrefied seed cake devolatilised earlier, had a more dispersed flame and higher NO formation. The higher reactivity of the biomass was shown to have a positive effect on the devolatilisation rate of the less reactive coal under co-firing simulations

Stator and rotor vent modelling in a MVA rated synchronous machine

An investigation into the solution dependence of a conjugate heat transfer computational fluid dynamics (CFD) model of a synchronous generator, with respect to meshing, has been carried out. Utilising CFD as a tool for investigating the airflow and thermal performance of electrical machines is increasing. Meshing is a vital part of the CFD process, but its importance is often misunderstood or overlooked in the context of electrical machine analyses; partly due to the relative mesh independency of the finite element analysis (FEA) numerical method. This paper demonstrates how a relatively complex, aircooled generator CFD model can be considerably influenced by changes in the mesh. Flow rate, velocity and windage effects are assessed as a function of the mesh adopted. Mesh changes have been shown to affect the mass flow rate through a single vent by up to 55% and the associated heat transfer coefficient by 128%

Fluid flow and heat transfer analysis of TEFC machine end regions using more realistic end-winding geometry

In this paper a typical small low voltage TEFC motor (output power ~10 kW) has been studied using computational fluid dynamics. The complexity of the end winding geometries, often consisting of several insulated copper strands bound together, provides a challenge to the modelling and analysis of heat transfer and fluid flow phenomena occurring in the end region which typically is an area of most interest for thermal management. Approximated geometries are usually employed in order to model the end windings to reduce analysis time and cost. This paper presents a comparison of two cases, a typical simplified geometry and a more realistic geometry of end windings and uses these cases to highlight the challenges and impact on predicted heat transfer. A comparison of the two models indicate that the different representations of end winding geometries can affect the heat dissipation rate through the outer housing by up to 45%

CFD optimisation of the thermal design for a vented electrical machine

Optimisation algorithms hold the potential to dramatically reduce computational time whilst ensuring the optimal solution is found. Within this paper, the feasibility of using this novel approach on complex 3-D Computational Fluid Dynamics models, which are required for thermal management of electrical machines, is proven. A model of a simplified generator is parameterised with the aim of minimising the peak stator temperature by varying the axial location of a single stator vent. By generating a single parameterised case, and automating the optimisation, the simulations are run independently after initial setup, hence reducing both computational and user time. Locating a vent in the optimal position reduced the peak stator temperature by 9.4 K. A sensitivity study linking peak temperature to vent position has been carried out developing a polynomial relationship between them for the aforementioned geometry. Mass flow and pressure distribution in the vent have been analysed in detail

Applicability of mechanical tests for biomass pellet characterisation for bioenergy applications

In this paper, the applicability of mechanical tests for biomass pellet characterisation was investigated. Pellet durability, quasi-static (low strain rate), and dynamic (high strain rate) mechanical tests were applied to mixed wood, eucalyptus, sunflower, miscanthus, and steam exploded and microwaved pellets, and compared to their Hardgrove Grindability Index (HGI), and milling energies for knife and ring-roller mills. The dynamic mechanical response of biomass pellets was obtained using a novel application of the Split Hopkinson pressure bar. Similar mechanical properties were obtained for all pellets, apart from steam-exploded pellets, which were significantly higher. The quasi-static rigidity (Young’s modulus) was highest in the axial orientation and lowest in flexure. The dynamic mechanical strength and rigidity were highest in the diametral orientation. Pellet strength was found to be greater at high strain rates. The diametral Young’s Modulus was virtually identical at low and high strain rates for eucalyptus, mixed wood, sunflower, and microwave pellets, while the axial Young’s Modulus was lower at high strain rates. Correlations were derived between the milling energy in knife and ring roller mills for pellet durability, and quasi-static and dynamic pellet strength. Pellet durability and diametral quasi-static strain was correlated with HGI. In summary, pellet durability and mechanical tests at low and high strain rates can provide an indication of how a pellet will break down in a mill

Fluid flow and heat transfer analysis of TEFC machine end regions using more realistic end-winding geometry

Here, a typical small low-voltage totally enclosed fan-cooled (TEFC) motor (output power ∼10 kW) has been studied using computational fluid dynamics. The complexity of the end-winding geometries, often consisting of several insulated copper strands bound together, provides a challenge to the modelling and analysis of heat transfer and fluid flow phenomena occurring in the end region, which typically is an area of most interest for thermal management. Approximated geometries are usually employed in order to model the end windings to reduce the analysis time and cost. This paper presents a comparison of two cases, a typical simplified geometry and a more realistic geometry of end windings, and uses these cases to highlight the challenges and impact on predicted heat transfer. A comparison of the two models indicate that the different representations of end winding geometries can affect the heat dissipation rate through the outer housing by up to 45%

Numerical investigations of convective phenomena of oil impingement on end-windings

A novel experimental rig for analysing intensive liquid cooling of highly power-dense electrical machine components has been developed. Coupled fluid flow and heat transfer has been modelled, using computational fluid dynamics (CFD), to inform the design of a purpose-built enclosure for optimising the design of submerged oil jet cooling approaches for electrical machine stators. The detailed modelling methodology presented in this work demonstrates the value in utilising CFD as a design tool for oil-cooled electrical machines. The predicted performance of the final test enclosure design is presented, as well as examples of the sensitivity studies which helped to develop the design. The sensitivity of jet flow on resulting heat transfer coefficients has been calculated, whilst ensuring parasitic pressure losses are minimised. The CFD modelling will be retrospectively validated using experimental measurements from the test enclosure