Turbulence measurements in decaying swirl flow in a pipe

Turbulence in decaying swirl flow through a pipe is studied experimentally by using a single rotating inclined hot-wire probe and the results are presented in the form of profiles of the three mean velocities and the six components of the stress tensor. The results indicate that all the nine components are very weakly influenced by the Reynolds number, but strongly depend on the initial swirl. The swirling stream develops two regions of flow which are characterized by the variation of the tangential velocity and the Reynolds stresses. It was also found that the turbulence intensities are higher at the core and with the decay of the swirl their magnitudes reduce markedly at the core while they change slightly near the wall.Nomenclature A, A₁–A₄ constants in equations (1–9) - B constant in equation (10) - C constant in equations (1–9) - D pipe diameter - E hot-wire anemometer output voltage - e fluctuating component of anemometer voltage - k yaw parameter - R pipe radius - r radial coordinate - S_n swirl number, 2 ₀^Ruwr²dr/R2 ₀^Rur²dr - (S_n)_in swirl number at inlet - T_m maximum moment of tangential velocity about axis, (W×Y)_max - U non-dimensional axial velocity, u/u_av - u, v, w time mean velocities in x, r and directions - u, v, w fluctuating components of velocity in x, r and directions - u_av average axial velocity - V non-dimensional radial velocity, v/u_av - v₁ instantaneous velocity vector - v_x, v_y, v_z instantaneous velocity components in x, y and z directions - W non-dimensional tangential velocity, w/u_av - W_max maximum tangential velocity at a section - x axial coordinate - Y non-dimensional radius, r/R - Y⁺ radius at which maximum tangential velocity occurs - probe angle - the angle between the wire axis and the instantaneous velocity vector - azimuthal angle of rotation of the probe about its axis