Publications

In this paper, the effect of cooling injection on the aerodynamics of tip flows in transonic turbines is investigated. Experiments are performed using an idealized model of a transonic tip flow. Schlieren photography, probe, and surface pressure measurements are used to determine the transonic tip flow structure and to validate the computational method. Computational simulations are performed to investigate the effects of cooling injection in a transonic blade environment. The results show that cooling injection has the potential to reduce overtip leakage loss.

In this paper, we investigate the real gas flows which occur within organic Rankine cycle (ORC) turbines. A new method for the design of nozzles operating with dense gases is discussed, and applied to the case of a high pressure ratio turbine vane. A Navier-Stokes method, which uses equations of states for a variety of working fluids typical of ORC turbines, is then applied to the turbine vanes to determine the vane performance. The results suggest that the choice of working fluid has a significant influence on the turbine efficiency.

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

n this paper the effect of blade-exit Mach number on unshrouded turbine tip-leakage flows is investigated. Previously published experimental data of a high-pressure turbine blade are used to validate a computational fluid dynamics (CFD) code, which is then used to study the tip-leakage flow at blade-exit Mach numbers from 0.6 to 1.4. Three-dimensional (3D) calculations are performed of a flat-tip and a cavity-tip blade. Two-dimensional calculations are also performed to show the effect of various squealer-tip geometries on an idealized tip flow. The results show that as the blade-exit Mach number is increased the tip-leakage flow becomes choked. Therefore the tip-leakage flow becomes independent of the pressure difference across the tip and hence the blade loading. Thus the effect of the tip-leakage flow on overall blade loss reduces at blade-exit Mach numbers greater than 1.0. The results suggest that for transonic blade rows it should be possible to raise blade loading within the tip

In this paper, a low order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three dimensional CFD method with multiple one-dimensional meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential non-uniformity. It also still maintains the desirable properties of being easy to set up and fast to run.

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