Publications

Design of Aerodynamically Balanced Transonic Compressor Rotors

This paper describes a simple and efficient physics-based method for designing optimal transonic multistage compressor rotors. The key to this novel method is that the spanwise variation of the parameter which controls the three-dimensional shock structure, the area ratio between the throat and the inlet, ‘Athroat /Ainlet’, is extracted directly from the 3D CFD. The spanwise distribution of the area ratio is then adjusted iteratively to balance the shock structure across the blade span. Because of this, the blade design will be called ‘aerodynamically balanced’. The new designmethod converges in a few iterations and is physically intuitive because it accounts for the real changes in the 3D area ratio that directly controls the shock structure. Specifically, changes in both the spanwise 3D flow and in the rotor’s operating condition; thus aiding designer understanding.

Authors:

Demetrios Lefas & Robert J. Miller

Publication:

ASME J. Turbomachinery

DOI:

10.1115/1.4063881

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Transonic Relief in Fans and Compressors

Every supersonic fan or compressor blade row has a streamtube, the “sonic streamtube,” which operates with a blade relative inlet Mach number of one. A key parameter in the design of the “sonic streamtube” is the area ratio between the blade throat area and the upstream passage area, Athroat/Ainlet. In this article, it is shown that one unique value exists for this area ratio. If the area ratio differs, even slightly, from this unique value, then the blade either chokes or has its suction surface boundary layer separated due to a strong shock. Therefore, it is surprising that in practice designers have relatively little problem designing blade sections with an inlet relative Mach number close to unity. This article shows that this occurs due to a physical mechanism known as “transonic relief.”

Authors:

Demetrios Lefas, Robert J. Miller

Publication:

ASME J. Turbomachinery

DOI:

10.1115/1.4052755

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Predicting the Operability of Damaged Compressors Using Machine Learning

Authors:

Taylor, J., Conduit, B., Dickens, A., Hall, C., Hillel, M., & Miller, R.

Publication:

ASME Turbo Expo 2019

DOI:

https://doi.org/10.17863/CAM.38691

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The Effect of Non-Equilibrium Boundary Layers on Compressor Performance

The paper investigates the effect of non-equilibrium behaviour of boundary layers on the profile loss of a compressor. The investigation is undertaken using both direct numerical simulation (DNS) of a mid-height section of a compressor blade and a reduced order model, MISES. The solutions are validated using experimental measurements made in the embedded stage of a multistage low speed compressor. The paper shows that up to 35% of the suction surface boundary layer of the compressor blade exhibits non-equilibrium behaviour. The size of this region reduces as the Reynolds number is increased. The non-equilibrium behaviour was found to reduce profile loss in most cases, however, in a range of cases where transition occurs through a small separation the presence of non-equilibrium behaviour was found to increase profile loss.

Authors:

Andrew P. S. Wheeler, Anthony M. J. Dickens, Robert J. Miller

Publication:

Journal of Turbomachinery

DOI:

10.1115/1.4040094

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Design of Compressor Endwall Velocity Triangles

Authors:

Kiran Auchoybur, Rob Miller

Publication:

Journal of Turbomachinery

DOI:

10.1115/1.4035233

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Load alleviation technology for extending life in tidal turbines

Authors:

Young, A., Farman, J., and Miller, R.

Publication:

In proceedings of the International Conference on Renewable Energies Offshore, Lisbon, Portugal

Competing 3D Mechanisms in Compressor Flows

Authors:

Taylor JV, Miller RJ

Publication:

Journal of Turbomachinery

DOI:

10.1115/1.4034685

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Unsteady Gust Response of Tidal Stream Turbines

This paper investigates the limitations of 2D linear unsteady aerofoil theory for modelling the unsteady gust response of tidal stream turbines. Accurate unsteady load prediction is required to determine turbine life. Current state of the art design codes in industry use a single model, based on Theodorsen’s theory, to predict the response to all types of gust. This paper shows that different types of gust require different types of model. Vortical gusts, such as due to turbulence and shear flows, should be modelled using a combination of Sears’ and Horlock’s theories. Pressure gusts, such as those caused by free surface waves, should be modelled using Loewy’s theory. The accuracy of these models is examined using numerical predictions. The range of gusts likely to occur at real tidal sites is also examined. In most likely situations, pressure gusts cause variations in loads which can be modelled quasi-steadily,but vortical gusts must be modelled using the combined Sears/Horlock theory

Authors:

Sequeira, C., and Miller, R.

Publication:

In proceedings of the OCEANS'14 MTS/IEEE conference, St. John's, Canada

Loss Mechanisms in Tidal Stream Turbines

This paper explores the loss mechanisms critical to the operation of a tidal stream turbine. There is an upper limit to the amount of power that may be removed from a tidal stream. The designer may therefore aim to minimise the ratio of loss to useful power. Computational predictions were undertaken on a horizontal axis turbine. At design point, the total loss for this case was 69.2% of the useful power extracted. This may be broken down to different sources: rotor profile loss, structural loss, and wake mixing loss. Wake mixing loss is shown to dominate. It is shown that in addition to the ‘idealised’ radial variation of velocity through the wake there was also significant circumferential variation. This circumferential variation is responsible for ~one third of total wake mixing loss, while the remaining two thirds is due to radial variations. This result implies that wake mixing loss could be reduced by designing turbines which produce wakes with lower circumferential non-uniformity

Authors:

Sequeira, C., and Miller, R.

The Effect of Leading-Edge Geometry on Wake Interactions in Compressors

The effect of leading-edge geometry on the wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and a circular leading edge were tested on a controlled diffusion aerofoil stator blade. Experiments were undertaken on the stator suction surface; these included hotwire boundary-layer traverses, surface hotfilm measurements, and high resolution leading-edge pressure measurements. Steady computational fluid dynamics (CFD) predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For a blade with an elliptic leading edge (Blade A), the leading-edge boundary layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary layer indicated that the wake/leading-edge interaction for Blade

Authors:

A. P. S. Wheeler, A. Sofia and R. J. Miller

Publication:

Journal of Turbomachinery

DOI:

10.1115/1.3104617

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