THE TURBULENT WAKE OF A CIRCULAR-CYLINDER ROTATING ABOUT THE STREAMWISE AXIS

This paper presents measurements in the turbulent wake of a circular c ylinder rotating with its axis normal to the free-stream velocity; in other words, the axis of rotation was parallel to the streamwise direc tion. All three mean velocities and six Reynolds stresses were obtaine d at three positions downstream of the cylinder, with and without rota tion of the free-stream. Most emphasis is given to the latter results because of the better flow quality. The ratio of the circumferential v elocity of the cylinder to the free-stream velocity - the swirl number - had a maximum value of 0.6. Measurements for two combinations of th e free-stream and angular velocities showed the velocity deficit in th e wake to be a multi-valued function of the swirl number, implying tha t the rotation affected the separation of the cylinder's boundary laye r in a complex manner. In the turbulent wake, the rotation did not sig nificantly alter the magnitudes of the normal stresses, but caused lar ge changes to the shape of the profiles of the axial and cross-stream normal stresses. Eventually, the primary (cross-stream) shear stress b ecame almost entirely positive, but there was no corresponding change to the (cross-stream) gradient of the streamwise mean velocity. Despit e these alterations to the turbulence, the rotationally-activated gene ration terms in the Reynolds transport equations never dominated the t erms that are common to the wakes of rotating and non-rotating cylinde rs.