Numerical analysis of pulsating turbulent flow in planar and constricted channels

To assess the impact of separation flow on pulsating heat transfer, a numerical investigation is conducted to compare the thermal characteristics in both planar and constricted channels. The study examines steady and pulsating inlet flow conditions across a wide range of pulsation frequencies l_s⁺ = 3.2–14, providing insights into the distinct behaviors induced by separation effects. The turbulent Reynolds number Re_τ = 350 is set. Wall-resolved LES method implemented in OpenFOAM-8 is used to simulate complex flow phenomena. For the planar channel, pulsating flow enhances heat transfer by up to 7.49 % at l_s⁺ = 4.4, consistent with previous studies. Periodic changes in centerline velocity are observed, showing a 45-degree phase lag in near-wall flow behavior and wall shear stress at medium and high frequencies. In contrast, the constricted channel demonstrates over a 40 % increase in Nusselt number compared to the planar channel under steady inflow, with a maximum enhancement of 19.235 % at l_s⁺ = 4.4. Thermal performance improvement is localized at the leading edge and downstream separation region. The thermal enhancement coefficient η is more sensitive to pulsation in the constricted channel, increasing significantly at l_s⁺ = 3.2–14, while remaining stable in the planar channel. These findings suggest that pulsating flow, particularly at medium frequencies, offers superior performance in channels with separated flow, providing valuable insights for future engineering designs.