Synthetic and Continuous Jets Impinging on a Circular Cylinder

0505915 - ÚT 2020 RIV US eng J - Journal Article
Broučková, Zuzana - Trávníček, Zdeněk - Vít, T.
Synthetic and Continuous Jets Impinging on a Circular Cylinder.
Heat Transfer Engineering. Roč. 40, 13-14 (2019), s. 1111-1125. ISSN 0145-7632. E-ISSN 1521-0537
R&D Projects: GA ČR(CZ) GA16-16596S
Institutional support: RVO:61388998
Keywords : synthetic jet * cylinder * heat transfer
OECD category: Thermodynamics
Impact factor: 1.693, year: 2019
Method of publishing: Limited access
https://www.tandfonline.com/doi/full/10.1080/01457632.2018.1457245

Synthetic and continuous water jets impinging onto an electrically heated circular cylinder were experimentally investigated. The slot nozzle width was 0.36 mm, the cylinder diameter was 1.2 mm, and the cylinder-to-nozzle spacing related to the slot width was 5-21. Two optical methods were used: qualitative laser-induced fluorescence (LIF) visualization and laser Doppler vibrometry (LDV) measurements. Simultaneously with the optical experiments, the overall convective heat transfer from the circular cylinder was evaluated. The LDV quantified the velocity of the oscillating piezo-driven diaphragm at frequencies from 30 to 68 Hz. A majority of the study was performed at the near-resonant frequencies from 46 to 49 Hz. For all investigated jets, the Reynolds numbers based on the nozzle width ranged from 36 to 171. The LIF visualization revealed a dominant flow separation occurring on the windward cylinder side. This result is attributed to the effect of the miniscales, a relatively small ratio of the nozzle width to the cylinder diameter, and low Reynolds numbers. An increase in the Reynolds number changes the flow pattern from a steady jet-flow separation to a vortex shedding wake-flow regime. The heat transfer experiments were validated in a natural convection regime. An enhancement of the average Nusselt numbers by 4.2-6.2 times by means of the synthetic jets was quantified by comparison with the natural convection regime. A correlation for the average Nusselt number was proposed for both the continuous and synthetic jets.
Permanent Link: http://hdl.handle.net/11104/0298244