25 research outputs found
On the Relation between Small-scale Intermittency and Shocks in Turbulent Flows
AbstractHigh Reynolds number turbulence is characterized by extreme fluctuations of velocity gradients which can interact with shock waves in compressible flows. While these processes are traditionally thought to happen at very disparate range of scales, both turbulence gradients as well as shock gradients become stronger as the Reynolds number increases. Our interest here is to in- vestigate their relation in the high-Reynolds number limit. Our conclusion is that for intermittent turbulence with inertial range scaling exponents which grow more slowly than linear at asymptotically high orders, small-scale intermittency produces gradients which are commensurate with shocks. This result is interpreted in the context of shock-turbulence interactions where intermittency appears to be responsible, in part, for the holes observed in shocks from simulations and experiments. This effect is aided by the correlation between strong gradients and flow retardation ahead of the shock which is observed from analysis of our direct numerical simulation database of incompressible and compressible turbulence
Emergence of universal scaling in isotropic turbulence
Universal properties of turbulence have been associated traditionally with
very high Reynolds numbers, but recent work has shown that the onset of the
power-laws in derivative statistics occurs at modest microscale Reynolds
numbers of the order of 10, with the corresponding exponents being consistent
with those for the inertial range structure functions at very high Reynolds
numbers. In this paper we use well-resolved direct numerical simulations of
homogeneous and isotropic turbulence to establish this result for a range of
initial conditions with different forcing mechanisms. We also show that the
moments of transverse velocity gradients possess larger scaling exponents than
those of the longitudinal moments, confirming past results that the former are
more intermittent than the latter
Mach number and wall thermal boundary condition effects on near-wall compressible turbulence
We investigate the effects of thermal boundary conditions and Mach number on
turbulence close to walls. In particular, we study the near-wall asymptotic
behavior for adiabatic and pseudo-adiabatic walls, and compare to the
asymptotic behavior recently found near isothermal cold walls (Baranwal et al.
(2022)). This is done by analyzing a new large database of highly-resolved
direct numerical simulations of turbulent channels with different wall thermal
conditions and centerline Mach numbers. We observe that the asymptotic
power-law behavior of Reynolds stresses as well as heat fluxes does change with
both centerline Mach number and thermal-condition at the wall. Power-law
exponents transition from their analytical expansion for solenoidal fields to
those for non-solenoidal field as the Mach number is increased, though this
transition is found to be dependent on the thermal boundary conditions. The
correlation coefficients between velocity and temperature are also found to be
affected by these factors. Consistent with recent proposals on universal
behavior of compressible turbulence, we find that dilatation at the wall is the
key scaling parameter for this power-law exponents providing a universal
functional law which can provide a basis for general models of near-wall
behavior.Comment: 24 pages, 15 figures, Under consideration for publication in Journal
of Fluid Mechanic