A comprehensive experimental investigation of the effect of the Reynolds number on the degeneration law for turbulence generated by biplanar and wicker grids is carried out over a wide range of the grid geometry parameters and the flow velocity. It is established that an increase in the flow velocity leads to an increase in the turbulence intensity at a given distance from the biplanar grid and a decrease in the turbulence decay rate downstream of the grid. An empirical relation between the turbulence intensity behind the grid, on the one hand, and the relative distance x/M from the grid and the Reynolds number based on the grid rod diameter and the flow velocity at the grid mesh center, on the other hand, is proposed. For the same relative distance x/M from the grid the intensity of wicker-grid turbulence is higher than in the case of the flow past a biplanar grid.
The results of an experimental investigation of the effect of the streamwise pressure gradient in a turbulent boundary layer on the permissible height of the surface roughness of bodies in an incompressible fluid flow are presented. The permissible roughness Reynolds number for which the characteristics of the turbulent boundary layer remain the same as in the case of flow past a smooth surface is determined.
The results of a systematic experimental study of the integral scale of turbulence generated by manipulators, such as grids and honeycombs, are presented. On the basis of the statistical processing of a large body of the experimental data (for 29 grids and 19 honeycombs) the dependence of the turbulence scale behind a manipulator on the relative downstream distance and the Reynolds number is established. A technique for reducing honeycomb flow conditions to those of flow past an equivalent grid has been developed. This makes it possible to present the experimental data for grids and honeycombs in the same functional form.
The results of a systematic experimental study of the flow turbulence level effect on the heat transfer and Reynolds analogy coefficients over a wide range of the relevant parameters (the turbulence intensity and scale and the Reynolds number) are presented. The notion of the equivalent flow turbulence, which unifies the above-mentioned parameters, is introduced. It is established that the skin friction and heat transfer coefficients increase with the equivalent turbulence, while the Reynolds analogy coefficient remains unchanged.
The results of an experimental investigation of the mechanism of reducing surface friction by mounting thin plates — large-eddy break-up devices (LEBUs) — in a turbulent boundary layer parallel to the surface are given. The conditions under which the surface friction reduction is minimal are determined. It is shown that the presence of LEBUs in the turbulent boundary layer leads to a decrease in the frequency of decelerated-fluid ejection from the wall region into the outer region of the boundary layer.
The combined effect of the turbulence intensity ɛ, the turbulence scaleL, and the Reynolds number Re** on the surface friction coefficientc f in a turbulent boundary layer is studied. The dependence of the relative friction increment on the equivalent turbulence level ɛcq, which takes into account the simultaneous variation in ɛ,L and Re**, is determined. The threshold value ɛcq* below which the value ofc f does not depend on ɛcq is found.
The characteristics of honeycombs of different shapes and sizes used for reducing free-stream turbulence in wind tunnels have been experimentally investigated. The optimum geometric dimensions of the honeycomb and its optimum location in the wind tunnel necessary to ensure a minimum level of turbulence in the working section have been determined.
The results of an experimental investigation of the conditions of flow turbulence suppression with a set of screens, each of which operates in the optimum regime, are presented. Recommendations are made concerning the choice of the number of screens in the set, their geometric parameters and their location in the flow which guarantee the most efficient reduction of free-stream turbulence.
We present results from an experimental study into the influence exerted by a countersunk inlet section of a drainage orifice on the error in the measurement of static pressure.
