A direct numerical simulation of a temporally developing mixing layer with a passive scalar transport is performed for various Schmidt numbers (Sc = 0.25, 1, 4, and 8). Turbulent mixing is investigated near the turbulent/non-turbulent interface (TNTI), which is a layer consisting of the turbulent sublayer (TSL) and viscous superlayer (VSL). The irrotational boundary, which is close to the outer edge of the TNTI layer, is detected as the isosurface of small vorticity magnitude. The movement of fluid elements relative to the irrotational boundary movement is analyzed. Once the non-turbulent fluid is entrained into the VSL across the irrotational boundary by the viscous diffusion of vorticity, the fluid moves away from the irrotational boundary in the VSL in the normal direction of the irrotational boundary. After the fluid reaches the TSL, it is transported in the tangential direction of the irrotational boundary and is mixed with the fluid coming from the turbulent core (TC) region. The boundary between the TSL and VSL roughly separates the region (VSL) mostly consisting of the fluid entrained from the non-turbulent flow from the region (TSL) where the fluids from both the TC and non-turbulent regions coexist. Therefore, the scalar value in the VSL is close to the non-turbulent value especially for high Sc cases. Because of a large difference in the scalar between the TSL and VSL, a peak value of the conditional mean scalar dissipation rate appears near the boundary between the TSL and VSL independently of Sc.
We investigated the effect of consumption of a catechin-containing drink on body fat level and its safety in healthy adults. The beverage (250 ml/bottle) contained 215.3 mg of tea catechins mostly possessing a galloyl moiety, which included (-)-epigallocatechin gallate 74.6 mg, (-)-epicatechin gallate 34.1 mg, (-)-gallocatechin gallate 77.8 mg, (-)-catechin gallate 24.5 mg. We conducted a double-blind study with three parallel groups. Healthy subjects (98 men and 97 women) aged from 20 to 65 years old with 22.5 < body mass index (BMI) ≤ 30 kg/m 2 were assigned to consume 3 bottles of placebo drink (control group), 2 bottles of catechin-containing drink and 1 bottle of placebo drink (low-dose group), or 3 bottles of catechin-containing drink (high-dose group), per day at mealtimes for 12 week (daily consumption of catechins was 41.1, 444.3 or 665.9 mg respectively). Compared to the value at 0 week, consumption of two or three bottles of catechin-containing drink results in significant decrease in body weight and BMI at 8 and 12 or 4, 8 and 12 week, respectively. Body weight and BMI was significantly decreased in both catechin groups compared with the control group from 4 to 12 week. The measurements of abdominal fat areas indicated significant reduction of total fat area and visceral fat area in both catechin groups compared with the control group at 12 week. Thus our present observations suggest that consumption of a catechin-containing drink may be useful for the prevention of obesity-related disorders.
The enstrophy (ω2/2) and passive scalar (ϕ) transport near the turbulent/non-turbulent (T/NT) interface is investigated using direct numerical simulation of a planar jet with passive scalar transport. To take into account the interface movement, we derive the transport equations for the enstrophy and the scalar in a local coordinate system moving with the T/NT interface. The characteristics of the T/NT interface are analyzed for three interface orientations. The cross-streamwise edge and the leading edge face the cross-streamwise and streamwise directions, respectively, and the trailing edge is opposite to the leading edge. The propagation velocity of the T/NT interface is derived from the enstrophy transport equation in the local coordinate system. The T/NT interface propagates toward the non-turbulent region on average at the cross-streamwise and leading edges, whereas the trailing edge frequently propagates into the turbulent region. The conditional average of the enstrophy transport equation in the local coordinate system shows that viscous diffusion transports, toward the non-turbulent region, enstrophy, that is advected from the turbulent core region or is produced slightly inside the T/NT interface. Viscous diffusion contributes greatly to the enstrophy growth in the region very close to the T/NT interface. The transport equation for the scalar ϕ in the local coordinate system is used to analyze the scalar transport near the T/NT interface. The conditional average of the advection term shows that ϕ in the non-turbulent region is frequently transported into the turbulent region across the cross-streamwise and leading edges by interface propagation toward the non-turbulent region. In contrast, ϕ in the turbulent region is frequently transported into the non-turbulent region across the trailing edge. The conditional averages of the advection and molecular diffusion terms show that both the interface propagation and the molecular diffusion contribute to the scalar transport across the T/NT interface.
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