Analytical/experimental comparison of the axial velocity in trailing vortices

The axial velocity of a vortex is a parameter which is known to be strongly related to the vortex breakdown, yet to date a complete description of its physical origins has not been achieved. A series of experiments studying the vortex trailed from a NACA 0015 wing using stereoscopic particle image velocimetry is presented and the axial velocity studied in detail. The problem of centering the instantaneous vector fields is addressed showing a high sensitivity of the results from the centering method which is adopted. It is shown that a strong axial velocity excess exists and a linear relationship between the axial velocity and a circulation parameter of the vortex is shown. The experimental data are compared with the analytical descriptions of the velocity in the centre of a simplified vortex giving new insights of the viscous effects in the development of the axial flow

Near field structure of wing tip vortices

High spatial resolution experiments in the near field of a trailing vortex using a Stereoscopic Particle Image Velocimetry technique have been carried out. A NACA 0015 model with flat tip has been tested for several Reynolds numbers and angles of attack. An axisymmetric meandering of the vortex is observed and a discussion on the aperiodicity correction method has identified the helicity peak as the most convenient indicator of the vortex centre. The axial velocity in the centre of the vortex has been recorded always as an excess except for low angle of attack cases where intermittent peaks of excess and deficit are superimposed on a large patch of deficit velocity. The double vortex structure and the consequent double inflection in the tangential velocity profiles is also studied with reference to a vortex age parameter. At already 2 chords of distance from the trailing edge the profiles exhibit axisymmetric behaviour. A spiral structure of the vortex core has been reported as effect of the early stage of the rolling up and considerations on the rotation confirmed the high dependency of the initial phase of the rolling up with the tip shape. The square tip produces a strong asymmetry of the vortex core and an intense secondary vortex. Good agreement of the tangential velocity and the circulation profiles between the experiments and analytical vortex expressions has been observed. The results confirm the existence of a three-part vortex structure, namely an inner, a logarithmic and an outer region of the vortex where the former is affected by the initial vortex structure and the latter is not universal but shows a dependence on the angle of attack

Well-posed lateral boundary conditions for spectral semi-implicit semi-Lagrangian schemes : tests in a one-dimensional model

The aim of this paper is to investigate the feasibility of well-posed lateral boundary conditions in a Fourier spectral semi-implicit semi-Lagrangian one-dimensional model. Two aspects are analyzed: (i) the complication of designing well-posed boundary conditions for a spectral semi-implicit scheme and (ii) the implications of such a lateral boundary treatment for the semi-Lagrangian trajectory computations at the lateral boundaries. Straightforwardly imposing boundary conditions in the gridpoint-explicit part of the semi-implicit time-marching scheme leads to numerical instabilities for time steps that are relevant in today's numerical weather prediction applications. It is shown that an iterative scheme is capable of curing these instabilities. This new iterative boundary treatment has been tested in the framework of the one-dimensional shallow-water equations leading to a significant improvement in terms of stability. As far as the semi-Lagrangian part of the time scheme is concerned, the use of a trajectory truncation scheme has been found to be stable in experimental tests, even for large values of the advective Courant number. It is also demonstrated that a well-posed buffer zone can be successfully applied in this spectral context. A promising (but not easily implemented) alternative to these three above-referenced schemes has been tested and is also presented here

The effect of climate change adaptation strategies on bean yield in central and northern Uganda

This paper analyses the impact of adaptation to climate change on bean productivity on a micro-scale using instrumental variable techniques in a two-stage econometric model, using data collected from farming households in northern and central Uganda. We employed the bivariate probit technique to model simultaneous and interdependent adoption decisions, and the ordered probit to model the intensity of adaptation. We modelled the impact of adaptation using instrumental variables and the control function approach because of the potential endogeneity of the adaptation decision. The driving forces behind adoption of the two selected adaptation strategies were heterogeneous. Location-specific factors influenced the intensity of adaptation between the two study regions. The effect of adaptation was stronger for households that used a higher number of strategies, evidence that the two adaptation strategies need to be used simultaneously by farmers to maximise the positive impact of adaptation

Socio-Cultural Factors Influencing Uptake of Skilled Childbirth Services Among Women in Kaiti Division, Makueni District (Kenya)

Each year, over 500,000 women die from the complications of pregnancy and child birth, almost all of them in the developing countries. This trend can be addressed by increasing the rates of skilled care during childbirth. This study therefore sought to establish the socio-cultural factors influencing uptake of skilled childbirth care which has remained low in Kaiti Division. The researchers applied a descriptive cross-sectional study design which involved women of childbearing age (15-49 years). The study was conducted in March 2010 and had a sample size of 246 women which was randomly selected from the estimated target population of 12,077. The researchers applied both quantitative and qualitative approaches. The tests of significance employed included Fisher's exact test, chi-square, test and logistic regression. The study established that the proportion of women attended to by the skilled attendant within various age cohorts was higher (58.9%) amongst the youth/adolescent (15-24 years) (P-value = 0.091> 0.05, c2 10.915 df 6).). Skilled attendance declined among the grand-multiparas (para4 and above) from 7.7% in Para 4-5 to 2% in Para 6+ (P-value = .000<0.05, c2 34.888 df 3; Para 1(p =0.000, OR 28.391), Para 2-3 (p =0.000, OR 7.564), Para 4-5(p=0.030, OR 3.493) Further findings indicated that the principal decision maker (46.7%) on type of assistant in the last delivery was the woman (P-value = 0.000 <0.05, c2 56.076 df 5). However, the husband was the leading (39.5%) decision maker in use of a skilled assistant in the last delivery (p=0.000, OR 15.667). More than two thirds (70.7%) of the respondents who performed a ceremony prayed for safe delivery in their last delivery. The study concluded that women's parity, decision making and religion were significant in use of skilled childbirth services

Job Satisfaction Among the Nurses of Makueni District Hospital, Kenya

The purpose of the study was to evaluate the level of job satisfaction among the nurses of Makueni District Hospital. This was necessitated by the high nurse staff turnover from the facility and a myriad of complains from various departments. The study was a cross sectional descriptive survey involving about 50 nurses that was carried out between 15 and 19th July 2013. The study employed mixed method approach. Tests of significance were through use of Chi-square, Fishers exact test and logistic regression. The key results were that overall job satisfaction was low (36%). There were significant relationships between job satisfaction and cordial relationship with the nurse manager (c2 12.131 df 4 p=0.016<0.05. Logistic regression p=0.018<0.05). The plans to quit the hospital and work elsewhere indicates a relationship with job satisfaction (c2 12.749 df 4 p=0.013<0.05). The findings of this study suggest that there is no enabling working environment for the nurses and this could be a barrier to service delivery in the Hospital. These findings suggest that the Nurse Managers should build up effective relationship with the staff and other departments and should identify negative working conditions which affect staff and appropriately delegate authority to them