Loss and deviation in windmilling fans

For an unpowered turbofan in flight the airflow through the engine causes the fan to freewheel. This paper considers the flow-field through a fan operating in this mode, with emphasis on the effects of blade row losses and deviation. A control volume analysis is used to show that windmilling fans operate at a fixed flow coefficient which depends on the blade metal and deviation angles, while the blade row losses are shown to determine the fan mass flow rate. Experimental and numerical results are used to understand how the loss and deviation differ from the design condition due to the flow physics encountered at windmill. Results are presented from an experimental study of a windmilling low-speed rig fan, including detailed area traverses downstream of the rotor and stator. 3D CFD calculations of the fan rig and a representative transonic fan windmilling at a cruise flight condition have also been completed. The rig test results confirm that in the windmilling condition the flow through the fan stator separates from the pressure surface over most of the span. This gene-rates high loss and the resulting blockage changes the rotor work profile leading to modified rotational speed. In the engine fan rotor, a vortex forms at the pressure surface near the tip and further loss results from a hub separation caused by blockage from the downstream core and splitter.EPSRCThis is the author accepted manuscript. The final version is available from ASME via http://dx.doi.org/10.1115/1.403316

Comparison of rectal and tympanic membrane temperature in healthy exercising dogs

The ability to monitor body temperature in athletes at risk of hyperthermia is essential in all species. Currently, the only commonly accepted temperature monitoring site in dogs is the rectum. This is impractical in field situations as it takes time, requires additional handlers to restrain the dog and is not tolerated by all animals. Tympanic membrane temperature (TMT) monitoring may provide a rapid measure of body temperature to facilitate identification of heat stress and heat stroke in canine athletes. In human studies, TMT diverges from rectal temperature (RT) as body temperature increases during exercise induced hyperthermia so is not recommended for monitoring human athletes. If the same divergence occurs in dogs, TMT may not be suitable for use when monitoring the temperature of canine athletes. The aim of the study was to determine if TMT diverged from RT following exercise in healthy dogs. 24 healthy dogs were recruited to the study. Body temperature was measured using a veterinary auricular infrared thermometer (VetTemp) to record tympanic membrane temperature and an electric predictive rectal thermometer. Temperatures were recorded pre and post exercise in a non-clinical setting, familiar to the dogs. The mixed model approach showed that exercise had no effect on the difference between RT and TMT (F(1,201) =0.026, P=0.872). The overall mean difference of RT minus TMT was 0.39°C (n = 116). 68.4% of readings fell within the accepted 0.5°C difference in temperature recording method. In line with previously reported TMT to RT comparison studies in dogs, this study found that TMT measured consistently lower than RT. Using a correction factor of 0.4°C minimised the difference. The hypothesis that dogs would show greater differences between TMT and RT following exercise was not supported, suggesting that TMT could be used to monitor body temperature in exercising dogs where RT is not possible

Using video to support veterinary nursing students preparing for OSCEs

Objective structured clinical examinations (OSCEs) inspire fear and loathing in both student veterinary nurses and clinical coaches alike. With different courses using different OSCE assessment criteria and different styles of assessment, students can find preparing for their OSCEs stressful and confusing if they receive different advice from difference sources. A further source of anxiety may be a perceived element of unfamiliarity with the equipment and resources likely to be present in the examination; if a student uses one type of centrifuge in practice, but then faces a different model in their OSCE this can trigger panic, and shaking hands may struggle to fill a capillary tube, especially with the added pressure of an examiner armed with a clipboard standing in attendance

Nonaxisymmetric stator design for boundary layer ingesting fans

In a boundary layer ingesting (BLI) fan system, the inlet flow field is highly nonuniform. In this environment, an axisymmetric stator design suffers from a nonuniform distribution of hub separations, increased wake thicknesses, and casing losses. These additional loss sources can be reduced using a nonaxisymmetric design that is tuned to the radial and circumferential flow variations at exit from the rotor. In this paper, a nonaxisymmetric design approach is described for the stator of a low-speed BLI fan. First, sectional design changes are applied at each radial and circumferential location. Next, this approach is combined with the application of nonaxisymmetric lean. The designs were tested computationally using full-annulus unsteady computational fluid dynamics (CFD) of the complete fan stage with a representative inlet distortion. The final design has also been manufactured and tested experimentally. The results show that a 2D sectional approach can be applied nonaxisymmetrically to reduce incidence and diffusion factor at each location. This leads to reduced loss, particularly at the casing and midspan, but it does not eliminate the hub separations that are present within highly distorted regions of the annulus. These are relieved by nonaxisymmetric lean where the pressure surface is inclined toward the hub. For the final design, the loss in the stator blades operating with BLI was measured to be 10% lower than that for the original stator design operating with undistorted inflow. Overall, the results demonstrate that the nonaxisymmetric design has the potential to eliminate any additional loss in a BLI fan stator caused by the nonuniform ingested flow field.</jats:p

Stall Inception in a Boundary Layer Ingesting Fan

Jet engines with boundary layer ingestion (BLI) could offer significant reductions in aircraft fuel burn compared with podded turbofans. However, the engine fans must run continuously with severe inlet distortion, which is known to reduce stability. In this paper, an experimental study has been completed on a low-speed rig fan operating with a BLI-type inlet distortion. Unsteady casing static pressure measurements have been made at multiple locations during stall events. Steady-state, full-annulus area traverses have also been performed at rotor inlet and exit at a near-stall operating point. The reduction in stability caused by BLI is found to be small. It is found that with BLI the fan can operate stably despite the presence of localized regions where the rotor operating point lies beyond the stability boundary measured in clean flow. With the BLI-type distortion applied, the measured rotor incidence varies around the annulus due to nonuniform upstream velocity and swirl. The measured amplitude of unsteady casing pressure fluctuations just prior to stall is found to correlate with the circumferential variation of rotor incidence, suggesting that rotor incidence is a key variable affecting the creation and growth of flow disturbances. In regions of high incidence, disturbances resembling local flow separations are initiated. However, in regions of low or negative incidence, any disturbances decay rapidly. Full rotating stall with BLI occurs when high incidence regions are widespread enough to sustain disturbances which can propagate around the entire annulus.</jats:p

Field testing two animal-specific non-contact thermometers on healthy horses

This study investigated the accuracy of two animal specific non-contact infrared thermometers (Rycom and Thermofocus) when compared to rectal temperature in healthy horses. One hundred rectal and eye temperatures were measured in 22 horses. Fewer than 50% of the readings taken with the Thermofocus device were within ± 0.5°C of rectal temperature. Over 80% of eye temperature readings taken with the Rycom device were within ± 0.5°C of rectal temperature measured from the medial canthus region. The Rycom thermometer also appears to detect hyperthermia when measuring the left eye temperature; however, clinical patient testing is needed before its use can be recommended

Time-constrained scenario-based practical examinations (TSPEs) – an alternative to OSCEs?

Assessing clinical competence in medical professionals typically involves both work-based assessment and simulated clinical examinations. Student veterinary nurses are assessed through the Nursing Progress Log during placement, then by means of practical examinations – objective structured clinical examinations (OSCEs). Time-constrained scenario-based practical examinations (TSPEs) are adapted from traditional OSCEs, including assessment of similar practical skills, but by means of a single patient scenario. This article introduces the theory behind using TSPEs and covers practical considerations for course teams considering adopting this assessment style

HIV/AIDS prevalence among South African health workers

Introduction. Studies on HIV prevalence among health workers usually focus on occupational exposure to HIV. Little is known about HIV prevalence in this group. However, it is expected that HIV prevalence among health workers will reflect prevalence in their society. Objective. To determine HIV prevalence among South African health workers. Method. A stratified cluster sample was drawn of 5% of health facilities in South Africa (N = 222) representative of the public and private health sectors in South Africa. The sample was designed to obtain a nationwide representative sample of medical professionals and non-professional health workers. A subsample comprising health workers in four provinces was tested for HIV status. The Orasure HIV-1 device in combination with the Vironostika HIV UNI-Form II plus O enzyme-linked immunosorbent assay (ELISA) kits were used to collect oral fluid specimens for HIV testing. Results. Based on a sample of 721 health workers and a response rate of 82.5% (or 595 respondents), the study found that an estimated 15.7% (95% confidence interval (CI): 12.2 - 19.9%) of health workers employed in the public and private health facilities located in four South African provinces, were living with HIV/AIDS in 2002. Among younger health workers, the risk is much higher. This group (aged 18 - 35 years) had an estimated HIV prevalence of 20% (95% CI: 14.1 - 27.6%). Non-professionals had an HIV prevalence of 20.3%, while professionals had a prevalence of 13.7%. Conclusion. HIV prevalence among health workers in South Africa is high; this calls for the introduction of antiretroviral programmes targeting them. In addition, there is a need for the development of new policy regarding placement of infected health workers in tuberculosis (TB) wards, coupled with vigorous human resource planning to replace the health workers likely to die from AIDS. Infection control procedures also need to be reviewed. S Afr Med J 2004; 94: 846-850

Drugs, dogs, and driving: the potential for year-round thermal stress in UK vehicles

Background: Dogs are regularly transported or housed in vehicles, with guidelines for housing dogs suggesting that the ambient temperature should be maintained between 15°C and 24°C. Veterinary drugs are routinely stored and carried in vehicles providing ambulatory veterinary care. Non-refrigerated medications typically require storage between 8°C and 25°C. Aim: This study aims to investigate the potential for thermal stress associated with vehicular storage and transportation of drugs and dogs in a temperate climate, such as the United Kingdom. Methods: The study used data loggers to continuously record internal temperatures of four vehicles at 15-minute intervals over a two-year period, to investigate the effect of seasonality and time of day on the internal car temperature. Results: The internal car temperature ranged from −7.4°C to 54.5°C during the study period. Temperatures fell below 8°C every month, except June and July. The internal car temperature exceeded typical drug storage recommendations (>25°C) during every month, and exceeded the canine thermoneutral zone (>35°C) from April to September. Peak temperatures occurred between 14:00 and 17:00 hours. Conclusion: The results demonstrate the year-round potential for thermal stress of both dogs and drugs left in cars. Public awareness campaigns highlighting the risks of leaving dogs in hot cars are typically launched in late spring, but should consider launching earlier in light of these findings. Veterinary surgeons transporting drugs should take measures to ensure that drugs are stored within the manufacturer’s temperature range year-round. This will limit the potential for drug degradation and decreased efficacy

Establishing a reference range for normal canine tympanic membrane temperature measured with a veterinary aural thermometer

Studies have shown that tympanic membrane temperature (TMT) under reports body temperature when compared to rectal temperature. This could lead to misinterpretation of the TMT, if comparing the result to a rectal temperature range. The aim of this study was to establish a normal canine TMT reference range. 416 TMT’s were taken from 157 healthy dogs, in a range of ambient temperatures. The normal reference range for canine TMT was found to be 36.6-38.8°C. This range should be considered by pet owners and veterinary professionals when interpreting TMT measured with a veterinary aural thermometer, to avoid misinterpretation of the results