Newsletter 2020.3 Index
Theme : "The Conference of Fluid Engineering Division (March issue)”
Seiya NAKAZAWA, Takaaki SHIMURA, Akihiko MITSUISHI, Kaoru IWAMOTO and Akira MURATA
Skin friction drag is a dominant factor to cause energy loss in turbulent flows. Therefore, drag reduction in turbulent flows is of great significance for energy saving. Traveling wave control is acknowledged as one of the effective flow control techniques for drag reduction. In the present study, drag reduction effect of traveling wave control in turbulent pipe flow is experimentally investigated. Figure 1 shows the experimental devices. A pipe is made of a silicone rubber sheet of 0.3 mm thick in order to obtain a sufficient wall deformation amplitude and is set vertically. Three piezoelectric actuators are mounted in the upstream region of the test section as the vibration sources to generate downstream waves. Effective values of wave parameters for drag reduction are obtained by adjusting input parameters of the actuators. Figure 2 shows the dependence of drag reduction rate on the bulk Reynolds number. The drag reduction rate of 4.5% is obtained at the designed Reynolds number of 4800. Laser Doppler velocimetry is carried out in order to evaluate the control effect in the flow field. Figures 3 and 4 show the time-averaged streamwise velocity profiles and the profiles of root mean square (rms) value of the streamwise velocity fluctuations. When the traveling wave control is applied, the streamwise velocity becomes smaller near the wall, which indicates the drag reduction effect. The rms values of the streamwise velocity fluctuations in the controlled case is larger than those of the uncontrolled case. A three-component decomposition is applied to evaluate the flow field of the controlled case in detail. A periodic component is generated near the wall, whereas a random component decreases compared with the uncontrolled case. Thus, the influence of the traveling wave control on the turbulent flow field near the wall in a pipe is experimentally confirmed.
Turbulent Pipe Flow, Drag Reduction, Traveling Wave, Wall Deformation
Fig. 1 Schematic of experimental devices.
Fig. 2 Dependence of drag reduction rate on bulk Reynolds number.
Fig. 3 Time-averaged streamwise velocity profiles.
Fig. 4 Profiles of rms value of streamwise velocity fluctuations.