University of Bath

About: University of Bath is a education organization based out in Bath, Bath and North East Somerset, United Kingdom. It is known for research contribution in the topics: Population & Context (language use). The organization has 15830 authors who have published 39608 publications receiving 1358769 citations. The organization is also known as: Bath University.

Flow and heat transfer in rotating-disc systems

Abstract: This book addresses rotor-stator systems. Topics covered include: Basic Equations; Laminar flow over a single disc; Turbulent flow over a single disc; Heat transfer from a single disc; Rotor-stator systems with no superposed flow; Rotor-stator systems with a superposed flow; Heat transfer in rotor-stator systems; and Sealing rotor-stator systems: The ingress Problem.

The Holt-Winters Forecasting Procedure

Abstract: SUMMARY The Holt-Winters forecasting procedure is a simple widely used projection method which can cope with trend and seasonal variation. However, empirical studies have tended to show that the method is not as accurate on average as the more complicated Box-Jenkins procedure. This paper points out that these empirical studies have used the automatic version of the method, whereas a non-automatic version is also possible in which subjective judgement is employed, for example, to choose the correct model for seasonality. The paper re-analyses seven series from the Newbold-Granger study for which Box-Jenkins forecasts were reported to be much superior to the (automatic) Holt-Winters forecasts. The series do not appear to have any common properties, but it is shown that the automatic Holt-Winters forecasts can often be improved by subjective modifications. It is argued that a fairer comparison would be that between Box-Jenkins and a non-automatic version of Holt-Winters. Some general recommendations are made concerning the choice of a univariate forecasting procedure. The paper also makes suggestions regarding the implementation of the Holt-Winters procedure, including a choice of starting values.

Flexible flapping airfoil propulsion at low Reynolds numbers

Abstract: Water tunnel experiments on a flexible airfoil plunging with constant amplitude have been carried out for Reynolds numbers of 0 to 27000. Peaks in thrust coefficient at intermediate values of airfoil stiffness were observed at both zero and non-zero Reynolds numbers, indicating that a degree of flexibility is beneficial at low Reynolds numbers. Time-averaged velocity fields and momentum flux data revealed a broader, higher-velocity jet in cases of optimum airfoil stiffness. Stronger vortices, separated by a larger lateral distance, characterised the corresponding instantaneous velocity fields. The flexibility causes the airfoil to pitch passively; the phase angle of the pitch was found to lead the plunge. Pitch amplitude and trailing-edge amplitude were found to be single-valued functions of pitch phase angle. The shape characteristics of the airfoil could therefore be described by the pitch phase angle only. Thrust coefficient was found to be a function of only two parameters: Strouhal number and pitch phase angle. For each Strouhal number, a peak in thrust coefficient was observed at a particular value of the pitch phase angle. The optimum pitch phase angle was found to tend to a limit of 105±5 degrees at very large Strouhal numbers. A significant thrust benefit was observed over very stiff airfoils when the optimum flexibility is utilized.