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Turbulence models in computational fluid dynamics (CFD) aim to capture a complex phenomenon through simplified mathematical models. The models themselves range in terms of application, complexity and methodology. This work looked at a transitional model for Reynolds averaged Navier Stokes equations. In particular the focus was on the correlation based intemitency and momentum thickness Reynolds number (γ - R̅eɵt) model. The original model has high order correlations, that were determined and calibrated from flat plate tests of various pressure gradients. In this work the correlations were simplified to reduce the number of calibration coefficients and help in understanding the effect of each parameter. Flat plate test data, from the European Research Community on Flow, Turbulence and Combustion (ERCOFTAC) T3A series, were used to verify the lower order approximations through Open FOAM simulations. The open source CFD package OpenFOAM was used for its easy access to the base code. The reduced order model was then applied to a National Advisory Committee for Aeronautics (NACA) 0012 foil at a transitional Reynolds number of 360 000 as a means of validation. The reduced order, the original γ - R̅eɵt of and the fully turbulent k - omega shear stress transport (k - ω SST) turbulence models are compared over a range of angles of attack to highlight the difference between models. The proposed model reduced the runtime of simulation by approximately 6%. The reduction in model coefficients meant a step by step adjustment could be implemented to increase model accuracy. In addition the adjusted model increased the accuracy of drag prediction on a NACA0012 airfoil, while maintaining a similar lift prediction as the original. [ABSTRACT FROM AUTHOR]

Slip factor accounts for the deviation of the flow angle from the trailing edge blade angle at the exit of radial impellers. Accurate values are required to predict impeller torque and energy input. The slip factor prediction method for back-swept radial bladed impellers is based on the socalled single relative eddy (SRE) method, which is an approximation of the classical, two-dimensional analytical solution to the inviscid flow problem. The relatively accurate prediction of the slip factors of 19 impellers found in four data sets published since its formulation, shows the reliability of the SRE method. The characteristics of straight-bladed impeller layouts are explored and incorporated into the SRE method. It turns out that the SRE method as developed for logarithmic spiral blades predicts the inviscid flow slip factor of 42 different straight bladed impeller geometries accurately, when a correction for the critical radius ratio at low blade numbers is introduced. Predicted slip factor values are also compared to new experimental data for five different impellers with straight, back-swept blades, over a range of three blade angles and three blade numbers. Agreement is excellent near the flow coefficient corresponding to the volute design angle. [ABSTRACT FROM AUTHOR]

Numerous researchers have investigated various techniques to reduce loss in gas turbine engines. One such technique that has shown promise is endwall secondary flow control using non-axisymmetric endwall contouring. Previous steady state investigations have shown that the generic endwall contour designed for a cascade reduced the loss in a rotating turbine test rig. The current investigation was to determine if there were unsteady effects introduced by the contour at design and off design conditions. An experimental and numerical study was performed to investigate the rotor flow field for any unsteady changes to the rotor exit flow field. The investigation was performed at an increased loading condition, design and a decreased loading condition to determine how changes in operating condition altered the flow field. The experimental results showed that the velocity magnitude of the hub endwall secondary flow vortex system for the contoured rotor was reduced. The peak difference in oscillation of the flow was also reduced. The effect of the endwall contour reduced the over and under turning of the endwall secondary flow vortex system as well. The magnitude of the FFT at the blade passing frequency was reduced below midspan. [ABSTRACT FROM AUTHOR]

This study evaluates the performance of the BMT 120 KS micro gas turbine engine. The analysis involves matching the existing engine components as well as redesigned elements using engine characteristic maps. An experimental investigation was conducted to measure the baseline performance parameters of the engine. Analytical calculations were used to review the thermodynamic cycle of the engine. A numerical component sensitivity analysis was also used to evaluate the engine’s output. The performance predictions of the engine and its modifications showed good correlation with test results and available engine data. [ABSTRACT FROM AUTHOR]

As concern for the environment increases, so does the desire to reduce emissions and improve fuel efficiency. One avenue being investigated in the aerospace industry is the reduction in losses in a gas turbine engine through endwall contouring, which has shown some promise in improving efficiency. The current investigation was aimed at investigating the unsteady effects downstream of a rotor with a non-axisymmetric endwall contour originally designed for a cascade. Previous investigations (numerical and experimental) have shown that the endwall contour improved the turbine efficiency by reducing the cross passage secondary flows. The contour however had a detrimental effect on the tip flow. The current investigation found that there were negligible unsteady differences between the annular and contoured rotor, with the average comparing well to the steady state results. It was also found that the effects at the tip were due to the experimental blades untwisting during operation. [ABSTRACT FROM AUTHOR]

The behaviour during an exploration task and the response to a confinement stress of Arctic charr Salvelinus alpinus were evaluated. Behaviour of individuals during 90 min of exploration was classified into high and low activity. High-activity individuals had higher plasma cortisol levels following stress compared to low-activity individuals. This indicates that high- and low-activity individuals correspond to reactive and proactive stress-coping styles. Further, a pigmentation analysis showed that high-activity individuals had a higher number of carotenoid spots cm−2 than low-activity individuals. Thus, carotenoid pigmentation, as melanin pigmentation in other salmonids, could be linked to stress-coping style in S. alpinus. [ABSTRACT FROM AUTHOR]

Stress and aggression have negative effects on fish welfare and productivity in aquaculture. Thus, research to understand aggression and stress in farmed fish is required. The neuropeptides arginine-vasotocin (AVT) and corticotropin-releasing factor (CRF) are involved in the control of stress and aggression. Therefore, we investigated the effect of agonistic interactions on the gene expression of AVT, CRF and their receptors in juvenile rainbow trout (Oncorhynchus mykiss). The social interactions lead to a clear dominant-subordinate relationship with dominant fish feeding more and being more aggressive. Subordinate fish had an upregulation of the AVT receptor (AVT-R), an upregulation of CRF mRNA levels, and higher plasma cortisol levels. The attenuating effect of AVT on aggression in rainbow trout is proposed to be mediated by AVT-R, and the attenuating effect of the CRF system is proposed to be mediated by CRF., (© 2021. The Author(s).)

Carotenoid pigmentation in Salvelinus alpinus has been connected to stress responsiveness in earlier studies. This has, however, only been tested with time-consuming image analysis from photos. Here, we used quick visual categorization of carotenoid pigmentation to investigate the stress responsiveness of the extreme groups. The visually selected charr were then exposed to a net restraint stressor. Arctic charr with few spots also had a lower stress responsiveness compared to charr with many spots. Thus, visual selection could be used as a simple method within aquaculture., (© 2020 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Social interaction is stressful and subordinate individuals are often subjected to chronic stress, which greatly affects both their behavior and physiology. In teleost fish the social position of an individual may have long-term effects, such as effects on migration, age of sexual maturation or even sex. The brain serotonergic system plays a key role in coordinating autonomic, behavioral and neuroendocrine stress responses. Social subordination results in a chronic activation of the brain serotonergic system an effect, which seems to be central in the subordinate phenotype. However, behavioral effects of short-term acute activation of the serotonergic system are less obvious. As in other vertebrates, divergent stress coping styles, often referred to as proactive and reactive, has been described in teleosts. As demonstrated by selective breeding, stress coping styles appear to be partly heritable. However, teleost fish are characterized by plasticity, stress coping style being affected by social experience. Again, the brain serotonergic system appears to play an important role. Studies comparing brain gene expression of fish of different social rank and/or displaying divergent stress coping styles have identified several novel factors that seem important for controlling aggressive behavior and stress coping, e.g., histamine and hypocretin/orexin. These may also interact with brain monoaminergic systems, including serotonin.

Individually consistent behavioral and physiological responses to stressful situations (often referred to as coping styles) has been reported in many animal species. Differences in hypothalamic-pituitary axis reactivity characterize individuals, and it has been proposed that the glucocorticoid (gr) and mineralocorticoid (mr) receptors are fundamental in regulating coping styles. We sorted individuals into reactive and proactive coping styles by collapsing behavioral outputs from net restraint and confinement stress tests in a principal component analysis. We then analyzed plasma cortisol levels, serotonin neurochemistry and the relative mRNA expression of gr1 and mr in stressed individuals per coping style. Proactive fish were characterized as having a lower serotonergic activity and being more active under stress. In addition, proactive fish had higher hypothalamic gr1 and mr abundance and a higher mr/gr1 ratio, compared to reactive fish. We found no significant differences in cortisol or telencephalic mRNA, gr1 and mr expression, or their ratio. Brain MR and GR have been proven to have an important role in the appraisal, coping and adaptation to stressful stimuli, so that a higher expression of these receptors in proactive fish suggests increased tolerance and performance under stress, compared to reactive individuals. We present evidence of a conserved neuroendocrine mechanism associated with coping styles in a fish species which is ecologically very diverse and considered to be the most cold-adapted fish in freshwater. We propose that this may be a first step into exploiting this model in order to better understand climate-change related effects in sub populations and ecophenotypes., (Copyright © 2017 Elsevier Inc. All rights reserved.)

A wide range of biologically active pharmaceutical residues is present in aquatic systems worldwide. As uptake potential and the risk of effects in aquatic wildlife are directly coupled, the aim of this study was to investigate the relationships between stress by isolation, uptake and effects of the psychiatric pharmaceutical oxazepam in fish. To do this, we measured cortisol levels, behavioral stress responses, and oxazepam uptake under different stress and social conditions, in juvenile perch (Perca fluviatilis) that were either exposed (1.03μgl -1 ) or not exposed to oxazepam. We found single exposed individuals to take up more oxazepam than individuals exposed in groups, likely as a result of stress caused by isolation. Furthermore, the bioconcentration factor (BCF) was significantly negatively correlated with fish weight in both social treatments. We found no effect of oxazepam exposure on body cortisol concentration or behavioral stress response. Most laboratory experiments, including standardized bioconcentration assays, are designed to minimize stress for the test organisms, however wild animals experience stress naturally. Hence, differences in stress levels between laboratory and natural environments can be one of the reasons why predictions from artificial laboratory experiments largely underestimate uptake of oxazepam, and other pharmaceuticals, in the wild., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The effect of motorboat noise on stress responsiveness in Eurasian perch and roach was tested in field enclosure experiments. Perch showed elevated cortisol levels after one 30-min noise exposure but not when exposed to noise repeatedly for 11 days. Roach had higher cortisol levels when exposed to noise than without noise when short- and long-term experiments were pooled. Both species had more cortisol in enclosures with mixed species compared with single-species enclosures. Both species also had higher cortisol levels in the short-term compared with the long-term experiment. Thus, a stress effect of motorboat noise may decrease with time due to habituation.

Pigmentation often signals status and in general melanin-based pigmentation is indicative of aggression and stress resilience in vertebrates. This is evident in the salmonids Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) where more melanin spotted individuals are more stress resilient. However, in the salmonid Arctic charr (Salvelinus alpinus) it seems as if it is carotenoid-based pigmentation that signals aggression and stress resilience. In our study, social stress effects on carotenoid-based spots, and behavioural and physiological stress responses were investigated. Socially stressed individuals have more spots, and behavioural stress responses were associated with spots. Some of the results concerning physiological stress responses, such as plasma cortisol levels and monoaminergic activity, are associated with spottiness. Further, the earlier proposed lateralization of spots, with left side connected to stress responsiveness and right side to aggression, is to some extent validated although not conclusively. In conclusion, this study provides further evidence that more stressed charr have more carotenoid spots, and for the first time monoaminergic activity is shown to be connected with carotenoid pigmentation., (Copyright © 2015 Elsevier B.V. All rights reserved.)