An experimental study on flow characteristics of turbulent pulsating flow in a curved duct by using LDV

In the present study, flow characteristics of turbulent pulsating flow in a square-sectional 180 .deg. curved duct were experimentally investigated. Experimental studies for air flows were conducted to measure axial velocity and wall shear stress distributions and entrance length in a square-sectional 180 .deg. curved duct by using the LDV with the data acquisition and the processing system. The experiment was conducted in seven sections from the inlet (φ = 0 .deg. ) to the outlet (φ =180 .deg. ) at 30 deg. intervals of the duct. The results obtained from the experimentation were summarized as follows ; (1) When the ratio of velocity amplitude (A1) was less than one, there was hardly any velocity change in the section except near the wall and any change in axial velocity distributions along the phase. When the ratio of velocity amplitude (A1) was 0.6, the change rate of velocity was slow. (2) Wall shear stress distributions of turbulent pulsating flow were similar to those of turbulent steady flow. The value of the wall shear stress became minimum in the inner wall and gradually increased toward the outer wall where it became maximum. (3) The entrance length of turbulent pulsating flow reached near the region of bend angle of 90 .deg., like that of turbulent steady flow. The entrance length was changed by the dimensionless angular frequency (ω+)