Relative importance of initial conditions on outflows from multiple fans

Area of Science:

• Fluid Dynamics
• Turbulence Research

Background:

• Generating homogeneous isotropic turbulence is essential for fundamental fluid dynamics research.
• Existing methods often struggle to achieve desired turbulence characteristics efficiently.

Purpose of the Study:

• To investigate the generation of homogeneous isotropic turbulence using a novel multifan wind tunnel.
• To determine the relative importance of initial conditions, specifically the number of phases (N) and shear magnitude (S), on turbulence development.

Main Methods:

• Utilized a multifan wind tunnel with 99 fans and a shear layer driving method.
• Introduced parameters N (number of phases) and S (shear magnitude) to characterize initial conditions.
• Numerically decomposed velocity fluctuations into periodic and nonperiodic components.
• Calculated energy spectra for nonperiodic data to analyze turbulence characteristics.

Main Results:

• The inertial subrange gradient of -5/3 widened with increasing N.
• Turbulence intensity of the nonperiodic component was highest for N=99, despite S being largest for N=2.
• Increasing N led to a wider inertial subrange.

Conclusions:

• The variety of shear layers (N) is more critical than the shear magnitude (S) for effective generation of high-Reynolds-number turbulence.
• The multifan wind tunnel shows promise for controlled turbulence generation.