A revisit of generalized scaling of forced turbulence through flux analysis

Abstract

In this investigation, we theoretically studied the transports of kinetic energy and scalar variance in turbulence driven by a scalar-based volume force in $M{\nabla}^{\beta} s'$ form associated with scalar fluctuations $s'$ in wavenumber space relies on flux conservation equation. The equation has one real solution and two complex solutions, which lead to four different cascade processes, including inertial subrange (constant fluxes of kinetic energy and scalar variance), CEF subrange (quasi-constant flux of kinetic energy), CSF subrange (quasi-constant flux of scalar variance), and a new subrange with both non-constant fluxes of kinetic energy and scalar variance in addition to dissipation subrange. ${\beta}$ controls the cascade processes and the scaling exponents. For the real solution, in the CEF subrange, ${\xi}_u$ is always -5/3, while ${\xi}_s=-(6{\beta}+1)/3$. In the CSF subrange, ${\xi}_u=(4{\beta}-11)/5$ and ${\xi}_s=-(2{\beta}+7)/5$ which are both consistent with the theory of Zhao and Wang (2021). Relying on ${\beta}$, the transport of kinetic energy and scalar variance can be distinguished as four cases. (1) When $\beta<3/2$ (except $\beta=2/3$), the CEF and CSF subranges are coexisted, with the former located on the lower wavenumber side of the latter. At ${\beta}=2/3$, a new inertial subrange with both ${\xi}_u$ and ${\xi}_s$ equal to -5/3 is present. (2) When $3/2<=\beta<2$, only the CEF subrange is predicted. (3) At $\beta=2$, special and singular exponents of ${\xi}_u=-1$, ${\xi}_s=-3$, ${\lambda}_u=1$, and ${\lambda}_s=-1$ can be found, if $MN=1$. Otherwise, a CSF subrange is predicted. (4) When $2<\beta<=4$, only the CSF subrange is predicted. Thus, a complete transport picture of both kinetic energy and scalar variance has been established for the type of forced turbulence.