Unstable wake dynamics of rectangular flat-backed bluff bodies with inclination and ground proximity

© 2018 Cambridge University Press. The paper investigates experimentally the global wake dynamics of a simplified three-dimensional ground vehicle at a Reynolds number of . The after-body has a blunt rectangular trailing edge leading to a massive flow separation. Both the inclination (yaw and pitch angles) and the distance to the ground (ground clearance) are accurately adjustable. Two different aspect ratios of the rectangular base are considered; wider than it is tall (minor axis perpendicular to the ground) and taller than it is wide (major axis perpendicular to the ground). Measurements of the spatial distribution of the pressure at the base and velocity fields in the wake are used as topological indicators of the flow. Sensitivity analyses of the base pressure gradient expressed in polar form (modulus and phase) varying ground clearance, yaw and pitch are performed. Above a critical ground clearance and whatever the inclination is, the modulus is always found to be large due to the permanent static symmetry-breaking instability, and slightly smaller when aligned with the minor axis of the base rather than when aligned with the major axis. The instability can be characterized with a unique wake mode, quantified by this modulus (asymmetry strength) and a phase (wake orientation) which is the key ingredient of the global wake dynamics. An additional deep rear cavity that suppresses the static instability allows a basic flow to be characterized. It is shown that both the inclination and the ground clearance constrain the phase dynamics of the unstable wake in such way that the component of the pressure gradient aligned with the minor axis of the rectangular base equals that of the basic flow. Meanwhile, the other component related to the major axis adjusts to preserve the large modulus imposed by the instability. In most cases, the dynamics explores only two possible opposite values of the component along the major axis. Their respective probability depends on the geometrical environment of the wake: base shape, body inclination, ground proximity and body supports. An expression for the lateral force coefficients taking into account the wake instability is proposed

Boat-tail effects on the global wake dynamics of a flat-backed body with rectangular section

© 2019 A three-dimensional body of rectangular section with a blunt trailing edge is studied for various angles of after-body boat-tailing. The Reynolds number of the flow is Re=4.0×105 and the body is in the vicinity of the ground. It is found that the wake dynamics is strongly dependent on the coupling of top and bottom boat-tail angles, triggering either long-time bi-stability between two mirror static asymmetric states or an anti-symmetric periodic mode, both leading to large cross-flow force fluctuations. The transition is shown to depend on the aspect ratio of the vertical base and not on the flow orientations imposed by the coupling of angles. Within the limitation of the aspect ratio for which the static states persist and dominate the wake dynamics, as boat-tails are installed at the after-body, they generate a vertical base pressure gradient component on which the static states adapt according to the mechanism proposed by Bonnavion and Cadot (2018)

Asymmetry and global instability of real minivans' wake

© 2018 Elsevier Ltd Three minivan cars tested in real flow conditions are investigated through base pressure distribution, force balance and velocity measurements. Discontinuous transitions of permanent wake reversals and bistable dynamics between two well-defined states are observed varying ground clearance, pitch and yaw, with open and closed air-intake. These transitions prove that the cars undergo the same global z-instability as the square-back Ahmed body (M. Grandemange, M. Gohlke and O. Cadot, Physics of Fluids, 25, 2013). The contribution of the global instability to the lift coefficient is estimated to 0.012 and 0.024 depending on the wake state. Eventually, the potential of direct passive control of the z-instability is demonstrated by improving from 4.6% to 8.3% the drag reduction obtained by closing the front air-intake of the car

Endothelial PlexinD1 signaling instructs spinal cord vascularization and motor neuron development

How the vascular and neural compartment cooperate to achieve such a complex and highly specialized structure as the central nervous system is still unclear. Here, we reveal a crosstalk between motor neurons (MNs) and endothelial cells (ECs), necessary for the coordinated development of MNs. By analyzing cell-to-cell interaction profiles of the mouse developing spinal cord, we uncovered semaphorin 3C (Sema3C) and PlexinD1 as a communication axis between MNs and ECs. Using cell-specific knockout mice and in vitro assays, we demonstrate that removal of Sema3C in MNs, or its receptor PlexinD1 in ECs, results in premature and aberrant vascularization of MN columns. Those vascular defects impair MN axon exit from the spinal cord. Impaired PlexinD1 signaling in ECs also causes MN maturation defects at later stages. This study highlights the importance of a timely and spatially controlled communication between MNs and ECs for proper spinal cord development

Circadian Clocks as Modulators of Metabolic Comorbidity in Psychiatric Disorders

Psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder are often accompanied by metabolic dysfunction symptoms, including obesity and diabetes. Since the circadian system controls important brain systems that regulate affective, cognitive, and metabolic functions, and neuropsychiatric and metabolic diseases are often correlated with disturbances of circadian rhythms, we hypothesize that dysregulation of circadian clocks plays a central role in metabolic comorbidity in psychiatric disorders. In this review paper, we highlight the role of circadian clocks in glucocorticoid, dopamine, and orexin/melanin-concentrating hormone systems and describe how a dysfunction of these clocks may contribute to the simultaneous development of psychiatric and metabolic symptoms

Tumour brain: pre‐treatment cognitive and affective disorders caused by peripheral cancers

People that develop extracranial cancers often display co-morbid neurological disorders, such as anxiety, depression and cognitive impairment, even before commencement of chemotherapy. This suggests bidirectional crosstalk between non-CNS tumours and the brain, which can regulate peripheral tumour growth. However, the reciprocal neurological effects of tumour progression on brain homeostasis are not well understood. Here, we review brain regions involved in regulating peripheral tumour development and how they, in turn, are adversely affected by advancing tumour burden. Tumour-induced activation of the immune system, blood–brain barrier breakdown and chronic neuroinflammation can lead to circadian rhythm dysfunction, sleep disturbances, aberrant glucocorticoid production, decreased hippocampal neurogenesis and dysregulation of neural network activity, resulting in depression and memory impairments. Given that cancer-related cognitive impairment diminishes patient quality of life, reduces adherence to chemotherapy and worsens cancer prognosis, it is essential that more research is focused at understanding how peripheral tumours affect brain homeostasis

Drag reduction using longitudinal vortices on a flat-back Ahmed body

AbstractThe paper presents different cavity wall designs at the rear of a flat-back Ahmed body to achieve drag reduction. The wake balance is assessed using the variance of the base pressure gradient and correlated to the obtained drag reduction. Without the rear cavity, the flat-back Ahmed body is subject to a steady instability producing a strong wake imbalance in the horizontal direction. The low drag rear design consists of a $$5^\circ$$ 5 ∘ inclined spoiler at the bottom (refered to as a diffuser) that first provokes a vertical imbalance and a non-inclined top spoiler with central imprints that re-balance the wake. The drag reduction is 11.5%, the wake structure is observed to respect the symmetry of the body base in both lateral and vertical directions suggesting a full stabilization of the initial steady instability. Both the wake balance and the stabilization are associated with the formation of a longitudinal vortex pair initiated at the imprint edges and penetrating the recirculating area.</jats:p

Gender-dependent regulation of G-protein-gated inwardly rectifying potassium current in dorsal raphe neurons in knock-out mice devoid of the 5-hydroxytryptamine transporter

Agonists at G-protein-coupled receptors in neurons of the dorsal raphe nucleus (DRN) of knock-out mice devoid of the serotonin transporter (5-HTT-/-) exhibit lower efficacy to inhibit cellular discharge than in wild-type counterparts. Using patch-clamp whole-cell recordings, we found that a G-protein-gated inwardly rectifying potassium (GIRK) current is involved in the inhibition of spike discharge induced by 5-HT1A agonists (5-carboxamidotryptamine (5-CT) and (\ub1)-2-dipropylamino-8-hydroxy-1,2,3, 4-tetrahydronaphthalene hydrobromide (8-OH-DPAT); 50 nM-30 \u3bcM) in both wild-type and 5-HTT-/- female and male mice. These effects were mimicked by 5\u2032-guanylyl-imido-diphosphate (Gpp(NH)p; 400 \u3bcM) dialysis into cells with differences between genders. The 5-HTT-/- knock-out mutation reduced the current density induced by Gpp(NH)p in females but not in males. These data suggest that the decreased response of 5-HT1A receptors to agonists in 5-HTT-/-mutants reflects notably alteration in the coupling between G-proteins and GIRK channels in females but not in males. Accordingly, gender differences in central 5-HT neurotransmission appear to depend-at least in part-on sex-related variations in corresponding receptor-G protein signaling mechanisms