Split Stream Flow Past a Blunt Trailing Edge with Application to Combustion Instabilities

In shear coaxial injectors, commonly used for cryogenic liquid rocket engines, propellants traveling at different velocities are separated by the inner jet post before they come into contact with each other, mix, and combust. Knowing how the fluids mix and how susceptible they are to hydrodynamic instabilities is paramount for a successful liquid rocket engine. In this study, the wake behind a blunt trailing edge of a long plate, similar to an unwrapped coaxial injector, was studied in a water tunnel. Two fluid streams of different velocities were introduced on opposite sides of the plate. PIV was used to visualize and determine the influence of the velocity ratio of the split stream on the wake behavior. Measurements of the vortex shedding frequency were taken at various velocity ratios and compared with well characterized cases with a uniform free stream. Operating conditions ranged from Reynolds number 6,000 to 22,000 and velocity ratios 0.30 to 1.00

Split Stream Flow Past a Blunt Trailing Edge with Application to Combustion Instabilities

In shear coaxial injectors, commonly used for cryogenic liquid rocket engines, propellants traveling at different velocities are separated by the inner jet post before they come into contact with each other, mix, and combust. Knowing how the fluids mix and how susceptible they are to hydrodynamic instabilities is paramount for a successful liquid rocket engine. In this study, the wake behind a blunt trailing edge of a long plate, similar to an unwrapped coaxial injector, was studied in a water tunnel. Two fluid streams of different velocities were introduced on opposite sides of the plate. PIV was used to visualize and determine the influence of the velocity ratio of the split stream on the wake behavior. Measurements of the vortex shedding frequency were taken at various velocity ratios and compared with well characterized cases with a uniform free stream. Operating conditions ranged from Reynolds number 6,000 to 22,000 and velocity ratios 0.30 to 1.00

DES study of blade trailing edge cutback cooling performance with various lip thicknesses

Three-dimensional detached-eddy simulation (DES) study has been carried out to evaluate the cooling performance of a trailing-edge cutback turbine blade with various lip thickness to slot height ratios (t/H). By adopting the shear-stress transport (SST) k-ω turbulence model, the numerical investigations were performed at two successive steps: first, to validate simulation results from an existing cutback turbine blade model with staggered circular pin-fins arrays inside the cooling passage against experimental measurements and other available numerical predictions; second, to understand the effects of the lip thickness to the slot height ratio on the blade trailing-edge cooling performance. It was found from the model validations that at two moderate blowing ratios of 0.5 and 1.1, DES predicted film cooling effectiveness are in very good agreement with experimental data. Further comparisons of four various t/H ratios (t/H = 0.25, 0.5, 1.0, 1.5) have revealed that the thermal mixing process between the ‘cold’ coolant gas and the ‘hot’ mainstream flow in the near wake region of the exit slot has been greatly intensified with the increase of the t/H ratio. As a result, it causes a rapid decay of the adiabatic film cooling effectiveness downstream of the blade trailing-edge. The observed vortex shedding and its characteristics in the near wake region are found to play an important role in determining the dynamic process of the ‘cold’ and the ‘warm’ airflow mixing, which in turn have significant influences on the prediction accuracy of the near-wall heat transfer performance. As the four t/H ratio increases from 0.25 to 1.5, DES predicts the decrease of main shedding frequencies as fs = 3.69, 3.2, 2.21, and 1.49 kHz, corresponding to Strouhal numbers St = 0.15, 0.20, 0.23, and 0.22, respectively. These results are in good agreement with available experimental measurements

Influência da interação touro x rebanho na estimação da correlação entre efeitos genéticos direto e materno em bovinos da raça Nelore Influence of sire x herd interaction on the estimation of correlation between direct and maternal genetic effects in Nellore cattle

A interação touro x rebanho foi avaliada em uma população com 30.789 registros de animais da raça Nelore nascidos entre 1984 e 1994 em doze fazendas localizadas em três Estados do Sudeste e Centro-Oeste brasileiro, com um total de 48.495 animais no pedigree. As características consideradas foram os pesos ao nascer (PESNAS) e à desmama (PESDES) e o ganho de peso da desmama ao sobreano (GP345). O efeito da interação touro x rebanho foi considerado aleatório em modelos animais uni e bicaraterística, usando MTDFREML. Esse efeito foi importante para PESNAS (6% da variância fenotípica) e influenciou os componentes de variância e covariância e, conseqüentemente, os parâmetros genéticos. O efeito foi menor (cerca de 1% da variância fenotípica) para PESDES, mas alterou as estimativas dos componentes de variância e covariância. Para GP345, o efeito foi pequeno, embora significativo pelos verossimilhança. As correlações genéticas entre efeitos direto e materno são próximas de zero, ou até mesmo positivas, se a interação touro x rebanho for incluída no modelo, e sempre negativas se ela for omitida.<br>Sire x herd interactions were studied in 30,789 records of birth (BW) and weaning weight (WW) and weight gain from weaning to 18 months of age (G345) of Nellore cattle born from 1984 to 1994 in twelve farms located in three states of central and southeastern Brazil, with a total of 48.495 animals in pedigree. Sire x herd interaction was considered as a random effect in single trait and two traits animal models using MTDFREML. This effect was important for BW (6% of the phenotypic variance) and it both affected variance and covariance components and, consequently, genetic parameters. The effect was smaller for WW (around 1% of the phenotypic variance), but influenced the estimates of (co) variance components. For G345, Sire x Herd effect was small. Likelihood tests showed that this effect was significant for all traits. This study showed that genetic correlations between direct x maternal effects are close to zero or even positive if sire x herd interaction is fitted in the model, and always negative if it is not

Produtividade acumulada como critério de seleção em fêmeas da raça nelore Accumulated productivity as selection criteria in nellore breed females

O presente trabalho teve por objetivo determinar os componentes de variância e estimar a herdabilidade da produtividade acumulada (PAC) de 15.070 fêmeas, criadas em diferentes rebanhos participantes do Programa de Melhoramento Genético da Raça Nelore. A PAC é um índice que considera a produção total de bezerros desmamados em kg, o tempo total de produção de bezerros e o início de parição. As análises estatísticas foram realizadas por meio do programa SAS (Statistical Analysis System) e os componentes de variância pelo método de máxima verossimilhança restrita utilizando o software MTDFREML. A média da PAC foi de 130kg de bezerros desmamados por vaca ao ano, e os efeitos do pai da vaca, rebanho e ano de nascimento da vaca foram significativos (P<0,0001) na variação dessa característica. O coeficiente de herdabilidade da PAC foi estimado em 0,15, indicando a existência de variabilidade genética suficiente para sua inclusão nos programas de melhoramento, o que resultaria na obtenção de fêmeas mais produtivas nos rebanhos.<br>This work had for objective to determine the variance components and to estimate the heritability of the accumulated productivity (ACP) of 15,070 females, reared in different participant herds of the Nellore Breeding Program. ACP is an index that considers the total production of calves weaned in kg, the total time of production of calves and the calving beginning. The statistical analyses were accomplished through the SAS program (Statistical Analysis System) and the variance components for the restricted maximum likelihood method using the software MTDFREML. The average of ACP was of 130kg of calves weaned by cow to the year, and the sire of cow effects, herd and year of the birth cow significatly (P<0.0001) affected in the variation of this characteristic. The coefficient of heritability of ACP was estimated in 0.15, indicating the existence of enough genetic variability for its inclusion in the improvement programs, what would result in the obtaining of more productive females in the herds

Estudo das associações genéticas entre perímetro escrotal e características reprodutivas de fêmeas Nelore Genetic association among scrotal circumference and female reproductive traits in Nellore

Os objetivos deste trabalho foram estimar parâmetros genéticos para as características perímetro escrotal (PE), medido aos 12 (PE12, n = 652) e 18 (PE18, n = 607) meses de idade, idade ao primeiro parto (IPP, n = 1582), datas do primeiro (DPP, n = 1582) e segundo partos (DSP, n = 644) e primeiro intervalo de partos (PIP, n = 644) de animais da raça Nelore. Os parâmetros foram estimados pelo método da máxima verossimilhança restrita, usando-se um modelo animal e incorporando 15.648 informações de pedigree. As estimativas de herdabilidade das análises incluindo somente uma variável foram 0,24±0,10; 0,31±0,10; 0,01±0,03; 0,11±0,05; 0,07±0,08; e 0,10±0,10, respectivamente, para PE12, PE18, IPP, DPP, DSP e PIP. Estas estimativas foram semelhantes às obtidas nas análises em que foram incluídas duas variáveis, com exceção da análise incluindo os dois PE (0,68 e 0,61 para PE12 e PE18, respectivamente). As estimativas de correlações genéticas entre PE12 e IPP, DPP, DSP e PIP foram, respectivamente, -1,00; -0,08; -0,71; e -0,37. Por outro lado, as correlações genéticas entre PE18 e as características observadas nas fêmeas foram, na mesma ordem, -1,00; 0,21; -0,35; e -0,44. A seleção para o PE12 seria mais efetiva que a seleção para o PE18, quando se deseja obter melhorias relacionadas às características reprodutivas das fêmeas.<br>The objectives of this work were to estimate of genetic parameters for scrotal circumference (SC) at 12 (SC12, n = 652) and 18 (SC18, n = 607) months of age, age at first calving (AFC, n = 1,582), first (FCD, n = 1,582) and second (SCD, n = 644) calving dates and first calving interval (FCI, n = 644) in Nellore cattle. Parameters were estimated using REML methodology, with animal models and considering the relations among 15,648 animals. Heritability estimates from univariate analyses were .24±.10, .31±.10, .01±.03, .11±.05, .07±.08 and .10±.10, respectively, for SC12, SC18, AFC, FCD, SCD and FCI. These values were close to the estimates from bivariate analyses, except for the analysis including both SC (heritability estimates of .61 and .68, respectively, for SC12 and SC18). Genetic correlation estimates between SC12 and, respectively, AFC, FCD, SCD and FCI were --1.00, -.08, -.71, and -.37. In the same order, genetic correlation between SC18 and female reproductive traits were --1.00, .21, -.35 and -.44. The selection for SC12 would be more effective than selection for SC18 when trying to improve the reproductive traits of the females