A novel approach to precessing jet stabilization: Design and heat transfer analysis

Originally developed to improve mixing efficiency in industrial burners, precessing jets have gained significant interest due to their wide range of applications, despite the challenges introduced by their inherent instability. To enhance control over the jet precessing motion, the present study introduces a novel precessing jet nozzle inspired by the feedback-channel mechanism characteristic of sweeping jets. The heat transfer performance of this device is examined using infrared thermography and the heated thin-foil heat flux sensor; the results are compared with those of a conventional precessing jet (CPJ). To characterize the heat transfer behaviour of the investigated precessing jets impinging on a foil, the Nusselt number distribution over the impingement surface is analysed at ten nozzle-to-foil distances, corresponding to normalized spacings z/d ranging between 1/6 and 3, being z the axial distance between the nozzle exit section and the foil and d the nozzle exit diameter. The Reynolds number is set to 1.55×104 for all the tests performed. Time-averaged analyses are performed for both jets, while phase-averaged analyses can be performed only for the stabilized precessing jet (SPJ). Indeed, its regular periodic motion allows phase identification, whereas the strong instability of the CPJ limits the investigation to time-averaged analysis. The findings reveal that the SPJ effectively stabilizes the precessing motion, generating a broader and more uniform Nusselt number distribution over the foil. In contrast, the CPJ generates higher Nusselt number values at all z/d, with higher heat transfer rates centred around the stagnation point, resulting in a less uniform Nusselt number distribution.