Measurement of turbulence characteristics in a closed volume with artificial turbulence

Summary

• 1. The characteristics of gas motion in a closed volume do not permit the use of an electrothermoanemometer with a single working filament to determine all three fluctuation velocity components along the coordinate axes in the general case of nonisotropic turbulence in the presence of a constant component. The approximate value of V′, if turbulence is almost isotropic, is 0.6–0.7 of the recorded value of the velocity V.

• 2. The quantitative determination of L₂ remains approximate, since the value of V′ is approximate. With increase in V′ there is a decrease in L₁ and in our chamber for air L₁=6–10 mm. L₁ depends on pressure as p^−0.4 and is slightly dependent on the molecular properties of the gas.

• 3. The Euler turbulence scale, determined from the fluctuation energy spectrum, is too low by a factor of 3–4 as a result of spectral distortions characteristic of a closed volume: whereas L₂≈ ≈2L₁ in a directional flow, in a closed volume spectral measurements give L_{2 meas}≈0.5–0.8 L₁.

• 4. In the case of turbulent combustion under conditions when L₁ exceeds the width of the zone of laminar combustion, heat and mass transfer is mainly realized by fluctuations considerably exceeding this width. The transfer under closed-volume conditions is proportional to the scale of the fluctuations to the power 4/3.