

The above image is actual data taken by a hot film anemometer probe at the exit of a Low Turbulence Inlet diffuser. As the suction through the porous diffuser is increased, the transition from turbulent to laminar flow is evident. Effects of Suction on Turbulence and Velocity Profiles: These two figures (click to enlarge) are turbulence and velocity profiles measured at the exit of a diffuser. The left figure shows turbulence reduction with increasing suction. Turbulence is eliminated for suction greater than and equal to 44%. The right figure shows the transition from a parabolic profile to a uniform profile also with increasing suction. Percent suction is defined as the ratio of mass flow removed by suction and the total mass flow entering the diffuser expressed as a percentage. Inertial Enhancements: Geometric expansion and suction cause streamline curvature. The inertia of larger particles cause them to deviate from the streamlines thus cause inertial enhancement. The laminar flow in the diffuser permits reliable computation of the enhancements as a function of aerodynamic diameter. For more information on the calculation of enhancement factors, please see the LTI Modeling page. 
