Publications

Modelling Turbine Acoustic Impedance

We quantify the sensitivity of turbine acoustic impedance to aerodynamic design parameters. Impedance boundary conditions are an influential yet uncertain parameter in predicting the thermoacoustic stability of gas turbine combustors. We extend the semi-actuator disk model to cambered blades, using non-linear time-domain computations of turbine vane and stage cascades with acoustic forcing for validation data. Discretising cambered aerofoils into multiple disks improves reflection coefficient predictions, reducing error by up to an order of magnitude compared to a flat plate assumption. A parametric study of turbine stage designs using the analytical model shows acoustic impedance is a weak function of degree of reaction and polytropic efficiency. The design parameter with the strongest influence is flow coefficient, followed by axial velocity ratio and Mach number. We provide the combustion engineer with improved tools to predict impedance boundary conditions.

Authors:

J. Brind, G. Pullan

Publication:

International Journal of Turbomachinery, Propulsion and Power

DOI:

10.3390/ijtpp6020018

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Effect of Blade Row Interaction on Rotor Film Cooling

The mechanisms of blade row interaction affecting rotor film cooling are identified to make recommendations for the design of film cooling in the real, unsteady turbine environment. Present design practice makes the simplifying assumption of steady boundary conditions despite intrinsic unsteadiness due to blade row interaction; we argue that if film cooling responds nonlinearly to unsteadiness, the time-averaged performance will then be in error. Nonlinear behavior is confirmed using experimental measurements of flat-plate cylindrical film cooling holes. Unsteady computations are used to identify the blade row interaction mechanisms in a high-pressure turbine rotor, and a quasi-steady model is used to predict unsteady excursions in momentum flux ratio. It is recommended that the designer should choose a cooling configuration that behaves linearly over the expected excursions in momentum flux ratio as predicted by a quasi-steady hole model.

Authors:

J. Brind, G. Pullan

Publication:

Journal of Turbomachinery

DOI:

10.1115/1.4047617

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The Effect of Isentropic Exponent on Transonic Turbine Performance

The isentropic exponent is one of the most important properties affecting gas dynamics. Nonetheless, its effect on turbine performance is not well known. This paper discusses a series of experimental and computational studies to determine the effect of isentropic exponent on the flow field within a turbine vane. Experiments are performed using a newly modified transient wind tunnel that enables annular cascade testing with a wide range of working fluids and operating conditions. For the present study, tests are undertaken using air, CO2, R134a, and argon, giving a range of isentropic exponent from 1.08 to 1.67. Measurements include detailed wall static pressures that are compared with computational simulations. Our results show that over the range of isentropic exponents tested here, the loss can vary between 20% and 35%, depending on vane exit Mach number.

Authors:

David Baumgartner, John J. Otter, Andrew P. S. Wheeler

Publication:

Journal of Turbomachinery

DOI:

DOI: 10.1115/1.4046528

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Toward Future Installations: Mutual Interactions of Short Intakes With Modern High Bypass Fans

In this paper, we investigate the coupled interaction between a new short intake design with a modern fan in a high-bypass ratio civil engine, specifically under the off-design condition of high incidence. The interaction is expected to be much more significant than that on a conventional intake. The performance of both the intake-alone and rotor-alone configurations are examined under isolation. Subsequently, a comprehensive understanding on the two-way interaction between intake and fan is presented. This includes the effect of fan on intake angles of attack (AoA) tolerance (FoI) and the effect of circumferential and radial flow distortion induced by the intake on the fan performance (IoF). In the FoI scenario, the rotor effectively redistributes the mass flow at the fan-face. The AoA tolerance of the short-intake design has increased by ≈4 deg when compared with the intake-alone configuration. Dynamic nature of distortion due to shock unsteadiness has been quantified. ST plots and p

Authors:

Nagabhushana Rao Vadlamani , Teng Cao , Rob Watson , Paul G. Tucker

Publication:

Journal of Turbomachinery

DOI:

https://doi.org/10.1115/1.4044080

Three-Dimensional Unsteady Hydrodynamic Modelling of Tidal Turbines

Authors:

Smyth, A., and Young, A.

Publication:

In proceedings from the 13th European Wave and Tidal Energy Conference, Napoli, Italy

DOI:

https://doi.org/10.17863/CAM.40077

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A Pneumatic Probe for Measuring Spatial Derivatives of Stagnation Pressure

This paper introduces a pneumatic 9-hole probe which can measure flow angles, stagnation and static pressures, and spatial derivatives of stagnation pressure. It does this through direct measurement at a single location, rather than empirical corrections using measurements at multiple points. The new design resembles a 5-hole probe with 4 additional holes positioned around the side of the probe head. This arrangement enables the probe to distinguish between flows with stagnation pressure gradient and flows at an angle. Mapping between the inputs, the probe hole pressures, and outputs, the calibration reference measurements, is achieved with a trained neural network which takes the place of a conventional calibration map.

Authors:

C.J. Clark, S.D. Grimshaw

Publication:

Proceedings of ASME Turbo Expo 2019

An unsteady pressure probe for the measurement of flow unsteadiness in tidal channels

An unsteady five-hole probe has been developed for the measurement of turbulent flow in tidal channels. Such measurements are vital for accurate prediction of unsteady loads on tidal turbines. Existing field-based velocimeters are either unable to capture the required range of frequencies or are too expensive to profile the variation of turbulence across a typical tidal power site. This work adapts the traditional five-hole wind tunnel probe to achieve a low-cost device with sufficient frequency range for tidal turbine applications. The main issue in the marine environment is that the ambient hydrostatic pressure is much higher than the dynamic pressure. This has been overcome by using novel calibration coefficients and differential transducers. In flume tank tests against laser Doppler velocimeter measurements, the frequency response of the probe has been shown to be sufficient to capture all the frequencies necessary for tidal turbine design.

Authors:

Young, A., Clark, C., Atkins, N., and Germain, G.

Publication:

IEEE Journal of Oceanic Engineering

DOI:

https://doi.org/10.1109/JOE.2019.2933131

Loss in Axial Compressor Bleed Systems

A new method for characterising bleed system loss is introduced, using research compressor test results as a demonstration case. A loss coefficient is defined for a control volume including only flow passing through the bleed system. The coefficient takes a measured value of 95% bleed system inlet dynamic head, and is shown to be a weak function of compressor operating point and bleed rate, varying by +/-2.2% over all tested conditions. This loss coefficient is the correct non-dimensional metric for quantifying and comparing bleed system performance.

Authors:

S.D. Grimshaw, J. Brind, G. Pullan, R. Seki

Publication:

Proceedings of ASME Turbo Expo 2019

Effects of stator platform geometry features on blade row performance

Authors:

Taylor, D.J. and Longley, J.P.

Publication:

Proceedings of Global Power and Propulsion Society Montreal, 7th-9th May 2018.

DOI:

10.5281/zenodo.1343388

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Improving tidal turbine efficiency using winglets

The cost effectiveness of a tidal stream turbine can be improved by maximising the power extracted for a given rotor diameter. This paper presents a numerical and experimental study showing that winglets could be used to this end. The numerical simulations were conducted using Tornado, a vortex lattice code, which can model the interaction between different spanwise sections unlike Blade Element Momentum methods. Tornado was used to identify the important winglet design parameters such as dihedral angle. Tornado cannot capture viscous effects and so an experimental study was conducted on four designs. These were tested on a small-scale horizontal axis turbine in the Ifremer ﬂume tank. The impact of winglets on the blade spanwise ﬂow was found to have a signiﬁcant effect on the amount of loss generated. The inviscid code used in this paper could complement existing quasi-3D design tools.

Authors:

Young, A. , Smyth, A., Bajpai, V., Augarde, R., Farman, J., and Sequeira, C.

Publication:

In proceedings from the 13th European Wave and Tidal Energy Conference, Napoli, Italy