Bursting detection by Variable-Interval Time-Averaging (VITA) on spanwise oscillated turbulent channel flow

Atilla Altıntaş,D Zhang,G Cui,H Ding,B Zi

doi:10.1051/matecconf/20167707002

Abstract

The main aim of the study is to detect the bursting phenomenon in spanwise oscillated Lorentz force applied turbulent channel flow. Regarding the biggest reason of the turbulence production is known as the bursting phenomenon, detecting the decrease on it could be a very effective tool as an estimation of the effectiveness of the applied control strategy to the flow. The data gained by DNS (Direct numerical simulations) at low Reynolds number ( Re τ = 180 based on the wall-shear velocity and channel half width). The Variable- Interval Time-Averaging (VITA) technique has been applied to three different streamwise locations for both applied force and no-force cases. The Lorentz force applied only to the lower wall. In first step the very well known drag reduction is observed, we compared the drag reduction results for the applied force and no-force cases both for the lower and upper wall of the channel. The bursting detection results are given statistically, which clearly shows that bursting phenomenon frequency tend to decrease as a result of the applied Lorentz force. It is also has shown that associated turbulence production has similar trend.

Highlights

The flow control studies are attracting a great attention since Prandtl successfully controlled a boundary layer [1], many numerical, experimental and theoritical studies are performed to control the drag in turbulent boundary layers [2,3,4,5,6,7]
This paper presents DNS simulations of channel flow (Reynolds number of 180) in which spanwise oscillating Lorentz force is applied along the spanwise direction
The spanwise oscillated Lorentz force is applied to the lower wall, which exhibits a significant drag reduction compare to upper, no-force applied wall

Summary

Introduction

The flow control studies are attracting a great attention since Prandtl successfully controlled a boundary layer [1], many numerical, experimental and theoritical studies are performed to control the drag in turbulent boundary layers [2,3,4,5,6,7]. Later some experimental studies performed which explored the possibility of achieving viscous drag reduction in turbulent boundary layers [9] An another important experimental study was later performed by [4], they placed the magnets and electrodes to direct the electromagnetic (EM) body force axially downstream and axially upstream. In these experiments a turbulence suppression up to 30% was achieved for the former case with the interaction parameter (S t ∼ O(1) is used, which represents the so-called “interaction parameter” is the ratio of the Lorentz force to the inertial force. With the body force axially upstream these researchers found an augmentation of the turbulence

Objectives

Results

Conclusion