1,721,121 research outputs found
ASPETTI MORFOLOGICI DEL PANCREAS DI TRITURUS CARNIFEX IN CONDIZIONI NORMALI E SPERIMENTALI, DOPO TRATTAMENTO CON ADRENALINA
No full textDrag reduction in a turbulent boundary layer with sinusoidal riblets
Full text linkWe report on an experimental investigation on the effect of sinusoidal riblets on the near-wall characteristics of a turbulent boundary layer. The investigated riblets are characterized by a fixed wavelength and two different values of the amplitude. We comment on the flow field organization via hot wire anemometry, planar and stereoscopic particle image velocimetry experiments; furthermore, we infer on the friction drag, directly measured with a load cell, comparing the sinusoidal riblets to the reference case of riblets aligned with the mean flow (longitudinal riblets) and the Smooth case.We show that the sinusoidal riblets generally yield higher drag reduction, attaining values as large as 10%, compared with the longitudinal riblets that are limited to 8% under the same conditions. We demonstrate that the drag reduction is associated with an overall attenuation of the turbulence intensity in the buffer layer. Furthermore, we provide statistical evidence of the fact that the sinusoidal riblets are responsible for an attenuation of the Reynolds shear stresses that contribute the most to turbulence production. From the detection of the accelerated events in the buffer layer, we show that the sinusoidal riblets lead to a weakening of the intensity of the events in the streamwise plane and an enhancement of the spanwise induced motion. We relate this mechanism to that responsible for drag reduction when using spanwise wall oscillations, suggesting a possible effect of a secondary alternating vorticity in the grooves of the sinusoidal riblets
understanding plant strategies and vulnerabilities demands a broader view for allelopathy scientists
No full textLarge-Scale Forcing of a Turbulent Channel Flow Through Spanwise Synthetic Jets
Full text linkThe investigation focuses on the forcing of a fully developed turbulent channel flow through a linear array of synthetic jets injected tangentially to the wall and orthogonal to the mean flow direction. Forcing configurations are varied by differently combining the number of actuated jets working in an opposing blowing–suction configuration. Instantaneous wall shear stress and streamwise velocity fluctuations evidence drag reductions as well as turbulence attenuation up to 20%. The forcing effects are persistent up to at least a 150 half-channel height downstream of the injection section. Particle image velocimetry investigations in planes perpendicular to the channel axis highlight the presence of a large-scale streamwise vortical structure covering the whole height of the channel. This structure is thought to be responsible for the significant drag reduction, which is similar to the typical behavior evidenced in the case of colliding jets. The nondimensional forcing frequency of the synthetic jets producing the maximum drag reduction and turbulence attenuation is 0.0074 for the investigated Reynolds number (Reτ=180). A statistical analysis of the near-wall structures demonstrates that the control mechanism acts in a way to reduce them in the forced configuration. It is conclude that the effect of the forcing is such that the near-wall structures merge and become less prone to inducing new structures, thus effectively reducing their number, and consequently the near-wall turbulence activity
Prelimunary data on cellular localization and on the effects of chromium and mercury on the growth and ultrastructure of protonemata from Funaria hygrometrica Hedw.
No full textStudies on Timmiella barbuloides (Brid.) Moenk., IV. SEM and TEM characterization of spore wall and first germination stages.
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