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This thesis aims to contribute to the understanding of transitional flows in the blade boundary layers of axial compressors. Two experiments are described, the first examining in detail the transitional boundary layer on a simulated controlled-diffusion blade and the second surveying the mid-height flowfield in an embedded stage of a low-speed axial compressor. The velocity distribution on the simulated blade is identical to the Velocity distribution on the suction surface of the blades in the axial compressor. At 2 Reynolds numbers and 3 levels of freestream turbulence, a single hot wire was used to conduct a boundary layer survey on a simulated controlled-diffusion blade. Integral parameters of the boundary layers are explored to dene the length and nature of transition. At low Reynolds number there is a separated or near separated region at the leading edge which does not lead to turbulence. Transition covers a length of approximately 20% of the blade chord, starting between 20% and 30% chord. The position of transition is strongly influenced by the level of freestream turbulence. Most of the transition process occurs within the decelerating flow region which exists from 20% of the chord. At high Reynolds number, a leading edge separation bubble leads to transition within 2% of the blade chord. Abu-Ghannam & Shaws correlation for the start and length of transition was found to predict the start of transition well for attached flows, but could not be relied upon for separated flows. It is apparent that the correlation was not designed for the very strong Velocity gradients in the leading edge region, and probably not for separated flow. _ Three flow conditions in the axial compressor were used: design speed, peak efficiency, low Reynolds number at peak efficiency (the machine was slowed to one-quarter speed) and design speed near the stall. Using hot wires at mid-height, axial and circumferential velocity and turbulence information was obtained. Wakes and structure within wakes are visible in the turbulence and Reynolds stress distributions. The wakes of more than one upstream blade row are visible; the region where two wakes intersect gives some information about interaction between a stator blade Wake and a rotor blade boundary layer. Some information is available about the length scale 'distribution inside and outside wakes. Secondary flow in the axial-circumferential plane shows motion within wakes and a vortex in the near-stall flowfield, shed preferentially at one point in the blade-passing cycle.

Master of Science - Science / Axial line placement is one step in a method known as space syntax which is used in town planning to analyse architectural structures. This is becoming increasingly important in the quickly growing urban world of today. The field of axial line placement is an area of space syntax that has previously been done manually which is becoming increasingly impractical. Research is underway to automate the process and this research forms a large part of the automation. The general problem of axial line placement has been shown to be NP-complete. For this reason, previous research in this field has been focused on finding special cases where this is not the case or finding heuristics that approximate a solution. The majority of the research conducted has been on the simpler case of axial line placement in configurations of orthogonal rectangles and the only work done with convex polygons has been in the restricted case of deformed urban grids. This document presents research that finds two non-trivial special cases of convex polygons that have polynomial solutions and finds the first heuristic for general configurations of convex polygons.

<p>The valve plate/cylinder block interface in an axial piston pump is often subject to extreme pressures, which can cause wear of the valve plate and ultimately, failure of the pump. The purposes of this study were to: a) experimentally investigate the film thickness generated between a floating valve plate and cylinder block in situ using proximity probes, b) develop a model which can predict the motion, film thickness and pressures of the floating valve plate and corroborate with experimental results, c) investigate surface pockets to provide additional lubricant at the valve plate interface by measuring the flow velocities and cavitation areas in a thrust washer bearing, d) numerically investigate surface modifications of the floating valve plate to observe any changes in lubricant pressure, temperature, cavitation, or valve plate deformation. Two different test rigs were designed, developed and used to investigate the performance of axial piston pumps and surface pockets. The axial piston pump test rig (APTR) was designed to operate and measure the steady state conditions of an axial piston pump. The APTR utilizes three non-contact proximity probes to measure the valve plate motion and film thickness between the cylinder block at various speeds and pressures. A thrust washer test rig (TWTR) was developed to measure the cavitation areas and flow velocities of lubricant in a pocketed thrust washer using μPIV. Through a novel interpolation approach, the depths of the micro-particles in the bearing pocket were determined using an analytical model. Using this approach, the μPIV measured 2D velocity field was employed to develop a 3D velocity field, which illustrates the fluid motion inside a pocketed thrust bearing at various speeds and viscosities. A dynamic lubrication model was developed using the thermal Reynolds equation augmented with the JFO boundary condition and the energy equation to determine the pressure, cavitation regions and temperature of the lubricant at the valve plate cylinder block interface. The lubricating pressures were then coupled with the equations of motion of the floating valve plate to develop a dynamic lubrication model. The stiffness and damping coefficients of the floating valve plate system used in the dynamic lubrication model were determined using a parametric study. The elastic deformation of the valve plate was also considered using the influence coefficient matrix approach. The experimental and analytical motion of the valve plate were then corroborated and found to be in good agreement. 4 and 8 pocket designs were then added as surface modifications to the floating valve plate in the dynamic lubrication model. The addition of surface modifications improved the lubricating conditions at the valve plate/cylinder block interface and resulted in increased minimum film thicknesses and lowered lubricant temperatures at the same operating conditions.</p>

É analisado um critério de dimensionamento de máquinas de fluxo axiais subsônicas, baseado no coeficiente de pressão mínimo referente ao lado de sucção do perfil junto ao cubo do rotor, cpsmin, onde se faz sentir a influência dos diversos parâmentros geométricos envolvidos, como tipo de perfil, ângulo de montagem e solidez, nas características aerodinâmicas pretendidas. Utiliza-se um modelo potencial, formulado pelo método das singularidades, com ajustes posteriores através de dados experimentais existentes na literatura. São encontrados bons resultados de distribuição de pressão e coeficiente de sustentação para perfis NACA série 65 arranjados em grade. Para verificação da aplicabilidade do critério em estudo são construidos e ensaiados cinco ventiladores axiais, com diferentes valores dos parâmetros geométricos. Conclui-se pela validade do critério, como indicador da geometria adequada para o dimensionamento de máquinas de fluxo axiais subsônicas.

An axial compressor for a domestic appliance can be designed to be smaller than an equivalent centrifugal compressor. However, the performance of such a compact axial compression system is limited by increased viscous losses and reduced flow turning at low Reynolds numbers ($Re$). In domestic appliance compressors, $Re$ is typically in the range $10^4$ - $10^5$. Although the aerodynamics of isolated aerofoils operating at these $Re$ have been studied extensively, the flow fields within low $Re$ axial compressors have not been investigated in detail. This dissertation aims to develop an improved understanding of loss variation at low $Re$ and to explore how the losses can be reduced through design changes. Experiments on a 5 times scaled-up single stage axial compressor have been conducted across a range of $Re$ of $10^4$ - $10^5$. The flow field has been characterised using detailed area traverses with a miniaturised five-hole probe at the rotor inlet, rotor exit and stator exit and a miniature hot-wire at the rotor exit. The probe was specifically designed and calibrated for the scale of the experiments and methods to improve the accuracy of the measurements have been applied including a probe geometry correction. The traverse experiments were performed at the design operating condition ($\phi=0.55$ and $Re= 6\times10^4$) and at a condition close to stall for a datum stage design, a stage with an improved stator design and two stators with compound lean. It was found that losses in the rotor were greater than the stator losses across the whole range of $Re$. As expected, the loss decreased with increasing $Re$ for both the stator and rotor. The losses were also increased by three-dimensional flow, with typical loss coefficients at the hub and tip of the blade rows in the range of $20-30\%$. A major contributor to the rotor loss was an unexpected hub separation that increased in size as $Re$ was reduced. At higher $Re$, the major loss sources were the rotor tip leakage, the stator wake and the stator hub separation. The results indicate that an improved stator design that accounts for the actual, measured, rotor exit flow field at low $Re$ could reduce the $Re$ at which blade row losses start to rise dramatically as well as reduce the loss across all $Re$. The improved stator design was better matched to the radial distribution of rotor exit flow angle, which led to a decrease in stator loss across all $Re$. For all stator designs, however, the measured stage stall margin was identical at all $Re$. This, along with the increase in velocity deficit in the rotor tip region at off-design indicates that stall occurred in the rotor and was neither $Re$ nor stator design dependent. The introduction of compound lean to the the stator design had the expected result of decreasing the endwall corner separation loss and increasing midspan losses. The experiments have shown that there was a loss increase in both the midspan and casing region much greater than the corresponding decrease in the stator hub. Also the mass flow redistribution in the experiments was larger that the redistribution predicted by the CFD. Three-dimensional RANS computations at low $Re$ of the same designs as experimentally studied were also conducted in order to investigate the predictive accuracy of industry standard CFD. The simulation results predicted the overall loss distribution but overestimated the end-wall losses and failed to capture the drop in stage performance at low $Re$. The differences with the experiments were caused by the inherent limitations of a fully turbulent solver that cannot reproduce transitional flow-features. Similarly to the experiments, there was no stall margin dependency on $Re$ in the simulations. This thesis has shown that with axial compressors designed specifically for low $Re$, the $Re$ at which the losses start increasing exponentially can be shifted from $10\times10^4$ to $ 4\times10^4$. The loss increase is predominantly caused by the rotor hub corner separation.

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 2010

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