Fluid flow in rotating low-specific-speed centrifugal impeller passage

Results from experimental investigations of the blade passage flow in a model pump impeller of low specific speed are described. It is found that the flow inside the rotating impeller passages is well described by the flow distribution postulated by potential-flow arguments and boundary-layer considerations. Using a custom-designed two-component laser-Doppler-velocimetry flow measurement system, mounted on a frame co-rotating with an impeller, the radial and circumferential velocity components of the relative flow inside an impeller passage were measured. Measurements were taken from blade to blade, and from this the passagewise fluid velocity was determined. The measured passagewise fluid velocity is compared to the potential-flow solution of the impeller passage-flow velocity that holds asymptotically in a region well away from the blade tips. Additional potential-flow finite-element calculations are used for comparison for those regions where the asymptotic expansion does not hold. The agreement between the experimental and theoretical values is seen to be good for the core flow region, which extends from the blade pressure side to the viscous boundary layer at the blade suction side. Furthermore, the calculation of the boundary-layer development along the suction side of the impeller blades is highlighted. Contrary to the blade pressure side, only there a significant departure from inviscid flow behaviour is observed. Calculations performed in the ordinary fashion, i.e. employment of the common thin-shear-layer approximation, substantiate the conception that for a low-specific-speed impeller the effects of spanwise rotation and modest surface curvature are accommodated in the description of the invisci

A Year-Long Large-Eddy Simulation of the Weather over Cabauw: An Overview

Results are presented of two large-eddy simulation (LES) runs of the entire year 2012 centered at the Cabauw observational supersite in the Netherlands. The LES is coupled to a regional weather model that provides the large-scale information. The simulations provide three-dimensional continuous time series of LES-generated turbulence and clouds, which can be compared in detail to the extensive observational dataset of Cabauw. The LES dataset is available from the authors on request. This type of LES setup has a number of advantages. First, it can provide a more statistical approach to the study of turbulent atmospheric flow than the more common case studies, since a diverse but representative set of conditions is covered, including numerous transitions. This has advantages in the design and evaluation of parameterizations. Second, the setup can provide valuable information on the quality of the LES model when applied to such a wide range of conditions. Last, it also provides the possibility to emulate observation techniques. This might help detect limitations and potential problems of a variety of measurement techniques. The LES runs are validated through a comparison with observations from the observational supersite and with results from the ‘‘parent’’ large-scale model. The long time series that are generated, in combination with information on the spatial structure, provide a novel opportunity to study time scales ranging from seconds to seasons. This facilitates a study of the power spectrum of horizontal and vertical wind speed variance to identify the dominant variance-containing time scales.Geoscience and Remote SensingCivil Engineering and Geoscience

Haulout site selection by southern elephant seals at Marion Island

Using data from an ongoing mark–resight programme at Marion Island, we tested  empirically whether southern elephant seals prefer certain terrestrial sites to others during the breeding, moulting and winter haulouts, and whether the pattern of site use is the same for different age and sex groups. Southern elephant seals preferred some sites, while discriminating against other sites, with different age and sex classes using different sites for certain haulout events. Wintering young animals did not show strong site selection. Some popular sites were used for all haulouts by all age and sex groups, and apparently have all the requirements of a good site for terrestrial haulout by southern elephant seals. Site selection becomes more apparent with age, suggesting the role of haulout experience in site selection.Key words: southern elephant seal, Mirounga leonina, Marion Island, age group, haulout, site selection

Errata: In the article ‘Haulout site selection by southern elephant seals at Marion Island’ that appeared in

ErrataIn the article ‘Haulout site selection by southern elephant seals at Marion Island’ that appeared in African Zoology 43(1):25–33 (April 2008), the institutional affiliations of the authors should have read:T.W. Mulaudzi1*, G.J.G. Hofmeyr1, M.N. Bester1, S.P. Kirkman1, P.A. Pistorius1,F.C. Jonker1, A.B. Makhado1, J.H. Owen2 & R.J. Grimbeek21. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, 0002 South Africa2. Department of Statistics, University of Pretoria, Pretoria, 0002 South Africa*Author for correspondence. Present address: National Zoological Gardens of South Africa, P.O. Box 754, Pretoria, 0002 South Africa.E-mail: [email protected]