Calculation of shock-separated turbulent boundary layers

Numerical solutions of the complete, time-averaged conservation equations using several eddy-viscosity models for the Reynolds shear stress to close the equations are compared with experimental measurements in a compressible, turbulent separated flow. An efficient time-splitting, explicit difference scheme was used to solve the two-dimensional conservation equations. The experiment used for comparison was a turbulent boundary layer that was separated by an incident shock wave in a Mach 2.93 flow with a unit Reynolds number of 5.7 x 10 to the seventh power m. Comparisons of predicted and experimental values of surface pressure, shear stress along the wall, and velocity profiles are shown. One of the tested eddy-viscosity models which allows the shear stress to be out of equilibrium with the mean flow produces substantially better agreement with the experimental measurements than the simpler models. A tool is thereby provided for inferring additional information about the flow, such as static pressures in the stream, which might not be directly obtainable from experiments

Shock waves and drag in the numerical calculation of isentropic transonic flow

Properties of the shock relations for steady, irrotational, transonic flow are discussed and compared for the full and approximate governing potential in common use. Results from numerical experiments are presented to show that the use of proper finite difference schemes provide realistic solutions and do not introduce spurious shock waves. Analysis also shows that realistic drags can be computed from shock waves that occur in isentropic flow. In analogy to the Oswatitsch drag equation, which relates the drag to entropy production in shock waves, a formula is derived for isentropic flow that relates drag to the momentum gain through an isentropic shock. A more accurate formula for drag, based on entropy production, is also derived, and examples of wave drag evaluation based on these formulas are given and comparisons are made with experimental results

Decay of far flow field in trailing vortices

A finite difference machine code is used in the wake vortex problems in the quasi-cylindrical boundary layer approximation. A turbulent energy model containing new features is developed that accounts for the major effects disclosed by more advanced models in which the parameters are not yet established. Several puzzles that arose in previous theoretical investigations of wake vortices are resolved

Association between Work-Related Hyperthermia Emergency Department Visits and Ambient Heat in Five Southeastern States, 2010-2012--A Case-Crossover Study

The objective of this study is to assess ambient temperatures\u27 and extreme heat events\u27 contribution to work-related emergency department (ED) visits for hyperthermia in the southeastern United States to inform prevention. Through a collaborative network and established data framework, work-related ED hyperthermia visits in five participating southeastern U.S. states were analyzed using a time stratified case-crossover design. For exposure metrics, day- and location-specific measures of ambient temperatures and county-specific identification of extreme heat events were used. From 2010 to 2012, 5,017 work-related hyperthermia ED visits were seen; 2,298 (~46%) of these visits occurred on days when the daily maximum heat index was at temperatures the Occupational Safety and Health Administration designates as having lower or moderate heat risk. A 14% increase in risk of ED visit was seen for a 1°F increase in average daily mean temperature, modeled as linear predictor across all temperatures. A 54% increase in risk was seen for work-related hyperthermia ED visits during extreme heat events (two or more consecutive days of unusually high temperatures) when controlling for average daily mean temperature. Despite ambient heat being a well-known risk to workers\u27 health, this study\u27s findings indicate ambient heat contributed to work-related ED hyperthermia visits in these five states. Used alone, existing OSHA heat-risk levels for ambient temperatures did not appear to successfully communicate workers\u27 risk for hyperthermia in this study. Findings should inform future heat-alert communications and policies, heat prevention efforts, and heat-illness prevention research for workers in the southeastern United States

Breeding Forage Grasses for Increased Heat Tolerance to Combat Climate Change

The onset of climate change brings many challenges for forage production in the southeastern United States, where it is projected to become hotter and dryer in the next century. To combat this climatic challenge, recurrent phenotypic selection was conducted in growth chambers on annual ryegrass (Lolium multiflorum Lam.) and orchardgrass (Dactylis glomerata L.) to select seedlings that can germinate and survive at temperatures of 40°C. Following three cycles of selection, germination was increased from \u3c 5% to 45% in annual ryegrass, and from 20% to 80% in orchardgrass. The rate of germination also increased, in both species by a factor of 8x that of the base germplasm. Realized heritability also increased by 40 – 45% for each species by the end of the project. This work successfully improved a quantitative trait using recurrent phenotypic selection using growth chambers as a stable environment and provided the basis for combatting climate change in other outcrossing forage species

Screening Annual Ryegrass for Increased Tolerance to Blast (\u3ci\u3ePyricularia oryzae\u3c/i\u3e)

Annual ryegrass [Lolium perenne L. spp. multiflorum (Lam.) Husnot] is a high-quality forage utilized heavily in the Southeast for pasture and grazing. Gray Leaf Spot (Pyricularia oryzae) is a fungal pathogen that infects gramineous species and is a common problem in perennial and annual ryegrass stands. This study was designed to screen for resistance to P. oryzae in the annual ryegrass cultivar Vertyl (PI 619473, FRA) and a heat-tolerant germplasm (HTARG5) derived from Marshall (PI 600770, USA) with intent to use recurrent phenotypic selection to crossbreed the two accessions. Marshall was also included as a susceptible reference cultivar. Two experiments were conducted, the first with 100 plants screened at 12-wk old and the second with 180 plants screened at 6-wk old. Plants were spray inoculated with a spore solution of 1 x 105 conidia mL-1 and incubated for 72h at 30:25°C (D:N), ≥85% RH. Percentage disease severity (DS) was assessed 3wk post inoculation by dividing the number of diseased leaves by the total number of leaves per plant. Germplasm accession was used as a main effect and was significant in both Exp. 1 (P=0.0341) and Exp. 2 (P=0.0036). For Exp. 1, mean DS was significantly greater in heat-tolerant germplasm (29.3) than Vertyl (19.4) (LSD = 8.1). For Exp. 2, mean DS for Vertyl, Marshall, and the heat-tolerant germplasm were 44.82, 61.02, and 62.55, respectively. Disease severity in Vertyl was significantly lower (LSD = 12.1) than both Marshall and the heat- tolerant germplasm. Mortality was also recorded, however, there was no significant difference between accessions for either experiment. These results confirm that Vertyl has significantly greater resistance to gray leaf spot than Marshall and can be a quality candidate for selection breeding

Identifying Forage Quality Eastern Gamagrass [\u3ci\u3eTripsacum dactyloides\u3c/i\u3e (L.) L.] Genotypes from a Wild Regional Collection

Eastern gamagrass is a perennial warm-season grass native to North America and endemic to the eastern United States. The species is highly valuable as both a forage and hay crop. In 2012, 171 wild-type eastern gamagrass accessions were collected from the southeast, mid-Atlantic and Atlantic coast regions. Each accession was relocated to Starkville, MS (33.423585, -88.792394) and established in a long-term nursery. Accessions were analyzed for ploidy level and during 2013-2014 were further evaluated for desirable forage characteristics including: cold tolerance, delayed maturity, rust resistance, and digestibility. Fourteen elite individuals were identified from the original collection and were propagated for further research. Elite genotypes were divided into individual proaxes and transplanted into a RCB design with three replications. Plots measured 3.04 m x 1.21 m with five replicate plants evenly spaced within the plot. Following a one-year establishment period, whole plots were harvested on a 28-day cycle from May to October. Plots were harvested to a 15 cm stubble height with a Wintersteiger Cibus S harvester. Following each harvest, nitrogen fertilizer was applied to all plots at 56 kg N ha-1 using urea ammonium sulfate (32-0-0-12S). Homogenized subsamples were taken to determine percent dry matter, neutral detergent fiber (NDF), acid detergent fiber (ADF), and in-vitro dry matter digestibility (IVDMD). The commercial cultivar ‘Highlander’, was included in the study as a check. Seasonal yields ranged from 1.19 - 2.73 Mg ha-1. Three accessions – originally collected in Alabama and North Carolina – produced significantly greater forage yield than the check (P \u3e 0.0001). Digestibility of the commercial check as well as one accession – collected in Tennessee – were significantly greater than all other accessions (P \u3e 0.0001)