| Title |
Flow Characteristics of a Turbulent Pulsating Flow in a Straight Duct Connected to a Curved Duct by using an LDV |
| Keywords |
Laser doppler velocimeter ; 레이져 도플러 유속계 ; Turbulent pulsating flow ; 난류맥동유동 ; Square duct ; 정사각 덕트 ; Entrance region ; 입구영역 ; Axial velocity ; 축방향 속도 ; Shear stress ; 전단응력 |
| Abstract |
In the present study, the flow characteristics of developing turbulent flows are investigated at the exit region of a square cross-sectional 180° curved duct with dimensions of 40mm×40mm×4000mm(height×width×length). Smoke particles produced from mosquito coils were used as seed particles for the LDV measurement. Experiments were carried out to measure axial velocity profiles, shear stress distributions and entrance lengths by using an LDV system and Rotating Machinery Resolver RMR with PHASE software. Experimental results clearly show that the time-averaged Reynolds number does not affect oscillatory flow characteristics because the turbulent components tend to balance the oscillatory components in the fully developed flow region. Also, the velocity profiles are in good agreement with 1/7 power law such as the results of steady turbulent flows. The turbulent intensity linearly increases along the walls and is slightly higher, especially in the period of deceleration. On the other hand, the LDV measurements show that shear stress values in slightly higher in the period of deceleration due to the flow characteristics in the exit region. The entrance length where flows become stable appears at the point that is 40 times the length of hydraulic diameter. |