Multiscale_turbulence
Multiscale turbulence
Class of turbulent flow
Multiscale turbulence is a class of turbulent flows in which the chaotic motion of the fluid is forced at different length and/or time scales.[1][2] This is usually achieved by immersing in a moving fluid a body with a multiscale, often fractal-like, arrangement of length scales. This arrangement of scales can be either passive[3][4] or active[5]
As turbulent flows contain eddies with a wide range of scales, exciting the turbulence at particular scales (or range of scales) allows one to fine-tune the properties of that flow. Multiscale turbulent flows have been successfully applied in different fields.,[6] such as:
- Reducing acoustic noise from wings by modifying the geometry of spoilers;[7]
- Enhancing heat transfer from impinging jets passing through grids;[8]
- Reducing the vortex shedding intensity of flows past normal plates without changing the shedding frequency;[9]
- Enhancing mixing by energy-efficient stirring;[10][11]
- Improving flow metering and flow conditioning in pipes;[12]
- Improving combustion.[13][14]
Multiscale turbulence has also played an important role into probing the internal structure of turbulence.[15] This sort of turbulence allowed researchers to unveil a novel dissipation law in which the parameter in
is not constant, as required by the Richardson-Kolmogorov energy cascade. This new law[15] can be expressed as , with , where and are Reynolds numbers based, respectively, on initial/global conditions (such as free-stream velocity and the object's length scale) and local conditions (such as the rms velocity and integral length scale). This new dissipation law characterises non-equilibrium turbulence apparently universally in various flows (not just multiscale turbulence) and results from non-equilibrium unsteady energy cascade. This imbalance implies that new mean flow scalings exist for free shear turbulent flows, as already observed in axisymmetric wakes[15][16]