Frictional resistance of turbulent pulsating air flow in a circular pipe

An experimental investigation is carried out for turbulent pulsating air flow characteristics in a circular pipe. The velocity and pressure drop measurements are used to analyze the effect of pulsation parameters on the flow resistance. The pulsating flow is generated by acoustic excitation in a pulsation chamber. The pipe length of 2 m with 15, 20, and 25 mm diameters is used. The Reynolds number varies from 5000 to 8000, at pulsation frequencies of 5-90 Hz (Wo=10-75) and amplitudes (A) of 20-50%. The spectral analysis of pulsating flow velocity at the center of pipe's exit reveals that at Wo=43-61, the flow exhibits higher turbulence, leading to increased flow resistance. For Wo<20-30, the turbulence induced by pulsations is minimal. When Wo>61, the flow becomes more coherent, resulting in reduced flow resistance. The highest increase in time-averaged pressure drop () typically occurs between Wo = 43-61 at a given A%. When the pipe diameter is changed while maintaining same Wo, turbulence levels are highest for smaller diameters, suggesting that the turbulent structures can penetrate toward the center of the pipe. Additionally, as the pipe diameter increases, the Wo at which begins to rise relative to the steady flow arrives earlier. A smaller diameter with higher pulsation amplitude reduced flow resistance, minimizing losses. The highest increase in time-averaged pressure drop () typically occurs between Wo = 43-61 at a given A%, which could enhance heat transfer or cleaning processes.