Department News
On the Drag Reduction in a Mirobubble-Laden Spatially-Developing Turbulent Boundry Layer
Seminar Date
2005-05-23
Author
임아주
Date
2005-05-23
Views
1928
1. 제 목 : On the Drag Reduction in a Mirobubble-Laden Spatially-Developing
Turbulent Boundary Layer
2. 연 사 : Professor S. Elghobashi
Department of Mechanical and Aerospace Engineering University of California, Irvine
3. 일 시 : 2005년 5월 27일(금) 오후 2시 30분 – 3시 25분
4. 장 소 : 301동 117호 세미나실
5. 내 용 : Experimental evidence during the past three decades indicates that injection of gaseous microbubbles (with diameter ranging from 1 to 1000 microns), and at a relatively large volume fraction (up to fv= 0.7) into a liquid turbulent boundary layer over a flat plate or axisymmetrical bodies can reduce the skin friction by as much as 80% from its value without bubble injection. However, the basic physical mechanisms responsible for that reduction were not fully understood.
The objective of our numerical (DNS) study is to explain the physical mechanisms responsible for the reduction of skin friction in a microbubble-laden, spatially-developing turbulent boundary layer over a flat plate, for Req = 1430 (or Rex = 800,000) and Req = 2900 (or Rex = 2,000,000). Our DNS results with microbubbles volume fraction ranging from fv = 0.001 to 0.02 show that the presence of bubbles results in a local positive divergence of the fluid velocity, divergence U > 0, creating a positive mean velocity normal to (and directed away from) the wall which, in turn, reduces the mean streamwise velocity and displaces the quasi-streamwise longitudinal vortical structures away from the wall. This displacement has two main effects:1. it increases the spanwise gaps between the wall streaks associated with the sweep events and reduces the streamwise velocity in these streaks thus reducing the skin friction by up to 20.2% for fv = 0.02, and2. it moves the location of peak Reynolds stress production away from the wall to a zone of a smaller transverse gradient of the mean streamwise velocity (i.e. smaller mean shear), thus reducing the production rate of turbulence kinetic energy and enstrophy.
6. 문 의 : 기계항공공학부 최해천 교수 ( 880-8361)
Turbulent Boundary Layer
2. 연 사 : Professor S. Elghobashi
Department of Mechanical and Aerospace Engineering University of California, Irvine
3. 일 시 : 2005년 5월 27일(금) 오후 2시 30분 – 3시 25분
4. 장 소 : 301동 117호 세미나실
5. 내 용 : Experimental evidence during the past three decades indicates that injection of gaseous microbubbles (with diameter ranging from 1 to 1000 microns), and at a relatively large volume fraction (up to fv= 0.7) into a liquid turbulent boundary layer over a flat plate or axisymmetrical bodies can reduce the skin friction by as much as 80% from its value without bubble injection. However, the basic physical mechanisms responsible for that reduction were not fully understood.
The objective of our numerical (DNS) study is to explain the physical mechanisms responsible for the reduction of skin friction in a microbubble-laden, spatially-developing turbulent boundary layer over a flat plate, for Req = 1430 (or Rex = 800,000) and Req = 2900 (or Rex = 2,000,000). Our DNS results with microbubbles volume fraction ranging from fv = 0.001 to 0.02 show that the presence of bubbles results in a local positive divergence of the fluid velocity, divergence U > 0, creating a positive mean velocity normal to (and directed away from) the wall which, in turn, reduces the mean streamwise velocity and displaces the quasi-streamwise longitudinal vortical structures away from the wall. This displacement has two main effects:1. it increases the spanwise gaps between the wall streaks associated with the sweep events and reduces the streamwise velocity in these streaks thus reducing the skin friction by up to 20.2% for fv = 0.02, and2. it moves the location of peak Reynolds stress production away from the wall to a zone of a smaller transverse gradient of the mean streamwise velocity (i.e. smaller mean shear), thus reducing the production rate of turbulence kinetic energy and enstrophy.
6. 문 의 : 기계항공공학부 최해천 교수 ( 880-8361)
