Vortex generators have been extensively employed in heat transfer systems to enhance thermal performance by promoting fluid mixing. However, the passive or self-oscillating flexible vortex generator (FVG) can suffer from a deflected mode that reduces thermal efficiency. To address this research gap, the present study investigates the dynamics and heat transfer characteristics of a FVG subjected to sinusoidal heaving motion at the leading edge, using the immersed boundary method. The effects of flag heaving frequency ( \(\varvec{f}_{\varvec{f}} = \mathbf {0.2}\) – \(\mathbf {1.0}\) ) and amplitude ( \(\varvec{A} = \mathbf {0.2}\) – \(\mathbf {1.0}\) ) on thermal performance are systematically analyzed. The results indicate that the dynamics of the flag are strongly dependent on both frequency and amplitude, with the drag coefficient increasing as these parameters rise. During the upstroke and downstroke phases, periodic vortex structures are observed in the downstream wake, closely correlated with the heaving frequency. These vortices disturb the thermal boundary layer, enhancing fluid mixing and heat transfer. Regarding heat transfer characteristics, mechanical energy loss increases with higher frequency and amplitude, consistent with the observed trends in drag coefficient. The system efficiency considerably improved compared to the baseline channel when the amplitude exceeds 0.6 and the frequency lies within the range of 0.2 to 0.5. Notably, optimal thermal enhancement is achieved at \(\varvec{f}_{\varvec{f}} = \mathbf {0.26}\) and \(\varvec{A} = \mathbf {1.0}\) , where system efficiency reaches 96%, compared to 80% in the absence of the FVG.
