Oblique and parallel modes of the bistable bluff body wake

Turbulent bluff body flows exhibit large-scale, low frequency dynamics associated with symmetry breaking in the wake which compromise stability and increase surface pressure drag. Previous tomographic PIV had detailed that these instabilities were associated with the stochastic reorientation of a hairpin featuring a near-base “head” connected to counter-rotating streamwise “tails” extending downstream. To better understand the associated flow physics, a half-axisymmetric bluff body is assessed by means of particle image velocimetry and pressure measurements. By application of proper orthogonal decomposition (POD) and an assessment of spanwise phase difference using a Morlet wavelet analysis, we show that the asymmetry of the wake region is intrinsically linked to a large scale circulation reversal responsible for the switch to the opposing symmetry breaking state. The antiphase relationship across the base is established by propagation of an oblique wave in the cross-stream direction at separation and as a result, the wake becomes twisted and skewed to one side inducing an asymmetric base pressure gradient. The two most energetic modes in the near wake are halved with respect to rectilinear bistable bodies; the first shows a helical topology with lateral asymmetry and the second shows a symmetry preserving condition with two counter rotating vortices at each side. Across the switch, the unsteady second mode briefly characterizes the wake. The associated parallel shedding regime with reduced asymmetry promotes axial motion (bubble pumping) which is coupled to an optimal, low drag condition.</p

Nutrition Risk, Resilience and Effects of a Brief Education Intervention among Community-Dwelling Older Adults during the COVID-19 Pandemic in Alberta, Canada

Up to two-thirds of older Canadian adults have high nutrition risk, which predisposes them to frailty, hospitalization and death. The aim of this study was to examine the effect of a brief education intervention on nutrition risk and use of adaptive strategies to promote dietary resilience among community-dwelling older adults living in Alberta, Canada, during the COVID-19 pandemic. The study design was a single-arm intervention trial with pre&ndash;post evaluation. Participants (N = 28, age 65+ years) in the study completed a survey online or via telephone. Questions included the Brief Resilience Scale (BRS), SCREEN-14, a brief poverty screen, and a World Health Organization-guided questionnaire regarding awareness and use of nutrition-related services and resources (S and R). A brief educational intervention involved raising participant awareness of available nutrition S and R. Education was offered via email or postal mail with follow-up surveys administered 3 months later. Baseline and follow-up nutrition risk scores, S and R awareness and use were compared using paired t-test. Three-quarters of participants had a high nutrition risk, but very few reported experiencing financial strain or food insecurity. Those at high nutrition risk were more likely to report eating alone, compared to those who scored as low risk. There was a significant increase in awareness of 20 S and R as a result of the educational intervention, but no change in use. The study shows increasing individual knowledge about services and resources in the community is not sufficient to change use of these services or improve nutrition risk