Anisotropy of turbulent flow behind an asymmetric airfoil

Feature of turbulent flow anisotropy behavior behind an asymmetric NACA 64-618 airfoil investigated in this paper. Experimental studies were performed using a hot-wire anemometery with X-probe at the chord-based Reynolds number $$1.7 \times 10^5$$ 1.7 × 10 5 . The average ensemble velocity and Reynolds stress components are used to determine the wake topology and anisotropy of turbulence. The obtained data allowed to identify the outside wake region, which is characterized by low instability and a high degree of anisotropy of the turbulent flow. This tendency is observed at different angles incident. Further, to gain better insight into the physics of this phenomenon the structure of turbulence have been evaluated. Integral turbulence length and time scales were estimated by the area of the autocorrelation function of velocity fluctuations. Then, using the second-order structural function, we obtained the dissipation characteristics of the flow. In addition, the features of the energy spectrum in the region with high and low degrees of turbulence anisotropy were analyzed.

Comparison of flow turbulence over a sand bed and gravel bed channel

Experiments were performed to examine the variations in flow turbulence with respect to sand and gravel bed channel. The 3D instantaneous velocity of water is measured by acoustic doppler velocimeter (ADV) at the test section which will provide an important data related to the flow turbulence. The parameters of turbulence measured that the vertical profiles of longitudinal velocity in flows with sand bed channel at the vicinity of bed surface are higher by 2–6% than flow subjected to gravel bed channel, while away from the boundary surface, it decreases by 5–10%. The variations of Reynolds shear stress increases by 35–50% with gravel bed channel, indicating higher exchange of flow energy towards the boundary and vice versa. The higher value is obtained for shear velocities by 58.5% and the von Karman's constant with gravel bed channel. The gravel bed channel influenced the turbulence intensities with higher magnitude in the streamwise and vertical direction. The present study also analysed the flow anisotropy, correlations coefficient and turbulence diffusivity and compared the results. The outcomes of the current work are beneficial for civil and hydraulic engineers, since the data of turbulence will advance the management of bed materials present in the river.

Experimental Investigation on Nonlinear Flow Anisotropy Behavior in Fracture Media

A series of flow experiments were performed on matched fractures to study the problem of non-Darcy flow in fractured media. Five rock fractures of different roughness were generated using indirect tensile tests, and their surface topographies were measured using a stereo topometric scanning system. The fracture was assumed to be a self-affine surface, and its roughness and anisotropy were quantified by the fractal dimension. According to the flow tortuosity effect, the nonlinear flow was characterized by hydraulic tortuosity and surface tortuosity power law relationships based on Forchheimer’s law. Fracture seepage experiments conducted with two injection directions (0° and 90°) showed that Forchheimer’s law described the nonlinear flow well. Both the proposed model and Chen’s double-parameter model gave similar results to the experiment, but the match was closer with the proposed model. On this basis, a new formula for the critical Reynolds number is proposed, which serves to distinguish linear flow and Forchheimer flow.