Influence Of External Turbulence Research Articles

BIO-INSPIRED CORRUGATED AIRFOIL AERODYNAMICS UNDER EXTERNAL TURBULENCE AT LOW REYNOLDS NUMBERS

Particle image velocimetry measurements have been undertaken to investigate the aerodynamic performance of bio-inspired corrugated airfoil under the influence of external turbulence. The study is motivated by the gliding flight of dragonflies and its relevance to bio-inspired corrugated wing design for micro air vehicles. The detailed flow-field measurements are undertaken at 6% turbulence intensity for six angles of attack (± 5°, ±10°, and 15°). The low Reynolds number regime from Re = 1200 to 13,200 corresponding to dragonfly flight has been covered in the current study. The aerodynamic performance of the corrugated airfoil is evaluated by obtaining drag and lift coefficients using modified wake survey method and Kutta-Joukowski theorem, respectively. The calculated C<sub>l</sub> and C<sub>d</sub> are compared with available literature, and it is noted that the performance of corrugated profile airfoil degrades significantly under the influence of external turbulence. The temporal wake obtained from the mean velocity fields is also presented for better visualization of flow dynamics. The findings of the study indicate that the performance of corrugated airfoil under external turbulence is strongly influenced by angle of attack at lower Re.

Effect of the Darrieus-Landau instability on turbulent flame velocity.

The propagation of turbulent premixed flames influenced by the intrinsic hydrodynamic flame instability (the Darrieus-Landau instability) is considered in a two-dimensional case using the model nonlinear equation proposed recently by Bychkov [Phys. Rev. Lett. 84, 6122 (2000)]. The nonlinear equation takes into account both the influence of external turbulence and the intrinsic properties of a flame front, such as small but finite flame thickness and realistically large density variations across the flame front. Dependence of the flame velocity on the turbulent length scale, turbulent intensity, and density variations is investigated in the case of weak nonlinearity and weak external turbulence. It is shown that the Darrieus-Landau instability influences the flamelet velocity considerably. The obtained results are in agreement with experimental data on the turbulent burning of moderate values of the Reynolds number.

VELOCITY OF TURBULENT FLAMELETS OF FINITE THICKNESS

Propagation of turbulent premised flamelets of finite thickness is considered using the model nonlinear equation proposed recently. The nonlinear equation takes into account both influence of external turbulence and intrinsic properties of a flame front caused by density variations across the front. The formula for the turbulent flame velocity is derived for the case of flamelets of small but finite thickness. The obtained results agree well with experimental data on flame propagation in a turbulent flow of moderate and high values of the Reynolds number. Known expressions for the flame speed found by Clavin-Williamsand by Yakhot for the case of zero thermal expansion of the fuel mixture are recovered.

Influence of External Turbulence on Heat Transfer in a Separated Flow Behind a Single Rib or a Step

Influence of External Turbulence on Heat Transfer in a Separated Flow Behind a Single Rib or a Step

Influence of external turbulence on flow in a rectangular cavity

This paper presents the results of an experimental investigation of the influence of external turbulence on a flow in a rectangular cavity.

Influence of external turbulence on the velocity field in the wake behind an ellipsoid of revolution

The velocity field in the wake behind an ellipsoid of revolution is numerically investigated on the basis of a second-order differential model as a function of the energetic and structural state of the external isotropic turbulence.

The influence of external turbulence on sheared interfaces

Abstract Experiments on the deepening of a sheared, turbulent, homogeneous layer downwards into a denser, homogeneous layer were conducted in an annular, laboratory tank, similar to, but larger than, that used by Kato and Phillips (1969). It was found that the entrainment rate did not scale on a Richardson Number containing the upper-layer depth as the length scale, but that all two-layer experiments do scale well on the product of a Richardson Number, gΔρW/ρU 2, and the ratio U/u∗, where W is a tank dimension and other symbols have their conventional meanings. This result shows that two velocity scales may be necessary to describe turbulent entrainment across a sheared interface.

The facilitated uptake of nitric oxide by haemoglobin in erythrocytes

Measurements of the rapid uptake of NO by haemoglobin in fresh erythrocytes have been made by constant-flow spectrophotometric observation of the amount of nitric oxide haemoglobin formed in a given time. Both for sheep and human erythrocytes a decay, from a high initial rate of uptake to a lower passive level, was found. The faster rate of uptake is proportional to the NO concentration and the form of the curves does not agree with advancing-front conditions. A comparison of NO and O 2 uptake by human cells, in these circumstances, indicated almost identical rates of uptake for the same concentration. The results are therefore incompatible with the simple passive model of diffusion through the cell membrane followed by diffusion through and chemical reaction with the internal haemoglobin. A model is proposed which depends on the flexibility of the erythrocyte. The fast rates correpond to the flexible form and water, carrying the gaseous ligands, is pumped to-and-fro as the cell membrane “flickers” under the influence of external turbulence. With the passive form the cell is considered to be relatively inflexible and unaffected by these external forces.