Active heat-transfer control by pulsed jet in a turbulent pipe flow at high Reynolds numbers

Control and enhancement of convective heat-transfer in wall-bounded turbulent flows, particularly in pipe flows, is crucial for many industrial applications. A common strategy to enhance heat-transfer is introducing controlled perturbations, such as Jets In Cross-Flow (JICF). Studies have shown that pulsed jets, actuated at specific frequencies and duty cycles, outperform steady jets. However, these findings are limited to a narrow range of Reynolds number, and studies at higher, industrially-relevant values are missing. This work extends the one of Castellanos et al. to higher Reynolds numbers, investigating the scaling of the optimal frequency. Experiments are conducted in a high-Reynolds number facility, namely the Long Pipe at the CICLoPE laboratory. Results show a peak heat-transfer enhancement at 150 Hz, which corresponds to a Strouhal number St = 6.3. At 75% duty cycle and 150 Hz, the pulsed jet outperforms steady-jet actuation, demonstrating enhanced heat-transfer with reduced mass-flow input. Further investigations will assess whether this optimal frequency scales with turbulence parameters as a function of Reynolds number.