3D experimental techniquesMulti-hot-wire & 3D-PTV

Arkady Tsinober, Alex LiberzonSchool of Mechanical EngineeringTel Aviv University IACAS48

The real motivation of this talk is to expose the experimental abilities

The main one is to demonstrate the Israeli Aerospace community the two experimental systems that have not been explored

The situation is such that the Turbulence Structure Laboratory has both experimental methods under one umbrella - ready for use

“Know how” (e.g. Marie Curie Chair in Fundamental Aspects of Turbulence)

http://www.eng.tau.ac.il/efdl

“ The velocity field is such a complicated function of space and time that a statistical description is easier than a detailed description. It is essentially three-dimensional, in the sense that the dynamical mechanism responsible for it (the stretching of vorticity by velocity gradients) can only take place in three dimensions; It is essentially nonlinear and rotational. A system of partial differential equations exists, relating the instantaneous velocity field to itself at every time and place.”

STEWART, 1963

The field of our study is turbulent flows characteristic of:

“I soon understood that there was little hope of developing a pure, closed theory, and because of the absence of such a theory the investigation must be based on hypotheses obtained in processing of experimental data...”

KOLMOGOROV, 1985

**http://www.eng.tau.ac.il/~tsinober/MarieCurieChair.htm

This quote helps to motivate the experimental research in turbulence

There are turbulent features that need 3D and time resolved measurements, e.g. vortex breakdown – abrupt, fast and unpredictable (at least in location or time)

Lagrangian approach is more “natural” to describe the flow

Describes motion of fluid parcels in Newtonian mechanics

“identity conservation law”: X(a,t), a ≡X(0)

Mixing, dispersion, diffusion Transfer of scalars, heat and mass Multi-phase flows with

“Lagrangian” phase: bubbles, particles, polymers

Eulerianvs

Lagrangian

Lagrangian approach is more difficult in some sense

The equations are nonlinear and non-integrable for “simple” flows

Pathlines (trajectories) are chaotic – difficult to track

No unique statistical relationship to “known” Eulerian quantities, e.g. mean, two-point correlation tensor

In Eulerian stationary flow Lagrangian can be unsteady, e.g. lack of homogeneity

Multi-hot-cold-wire anemometry

mean:U i , fluctuating: ui ,full gradient tensor :∂U i /∂ x j ,∂ui /∂ x jtemperature gradients :∂/∂ x j

The core is in the calibration

... and people

Recent measurement sessions: in the wind tunnel, Imperial College

Malloja pass, Italy-Switzerland Alps

Does acceleration scale as a local quantity – do we get closer to the solution?

Just to remind you that we use 3D-PTV

Great details from computations

Now also achievableby “streaks”3D-PTV

Intrinsic structure, 3D and small scale (“last but not the least”)

Field: Re ~ 104 3D-PTV, Re ~ 50

Before with DNS, now in the atmospheric boundary layer or in a lab

Lagrangian properties: alignments and correlations

The way to discover that vortex lines are NOT analogy to the material lines

Summary The experimental methods and systems have

been presented The general overview of their capabilities are

demonstrated Representative results are shown

Everybody are welcome to visit the lab and get an impression of the experimental facilities

Thank you