![Sample our Engineering & Technology journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5933/TOC-Subject-Sample-2021-Engineering-Tech.jpg"})
ABSTRACT
In this paper the effect of inlet velocity field excitation on heat transfer by an impinging round jet has been investigated using Large Eddy Simulations (LESs). The time-averaged bulk Reynolds number (Re) of the jet for all cases is 23,000 and the dimensionless jet’s outlet-to-target wall distance (H) is two diameters. The Strouhal number (St) corresponding to the preferred mode of the unexcited jet is estimated through LES. The jet is then excited at different frequencies. The amplitude of excitation is kept at 50% of the bulk inlet velocity. It has been found that the excitation of the jet velocity field causes only large-scale excitation. Heat transfer enhancement is found to be possible with inlet velocity field excitation.
Nomenclature
| AN | = | amplitude of excitation |
| bij | = | Reynolds stress anisotropy tensor |
| D | = | jet's diameter, m |
| fo | = | most amplified frequency, Hz |
| fn/2 | = | frequency half of the preferred mode |
| f2n | = | frequency twice that of the preferred mode |
| H | = | jet's outlet-to-target-wall distance, m |
| II,III | = | second and third invariants |
| L(t) | = | integral length scale at inflow plane, m |
| Nu | = | Nusselt number [–] |
| <Nu>avg | = | Nu averaged till r/D = 6 |
| <Nu>stg | = | Nu at stagnation point |
| Pr | = | molecular Prandtl number [–] |
| Prs | = | subgrid turbulent Prandtl number [–] |
| qw | = | constant heat flux per area W/m2 |
| Re | = | Reynolds number of the jet [–] |
| = | Strouhal number based on shear-layer thickness [–] | |
| StD | = | Strouhal number based on jet's diameter [–] |
| T | = | temperature, K |
| To | = | jet inlet temperature, K |
| Tw | = | target wall temperature, K |
| <u> | = | radial velocity component, m/s |
| <ui> | = | mean axial velocity, m/s |
| = | velocity fluctuations, m/s | |
| uτ | = | shear velocity ( |
| Ub | = | time-averaged bulk velocity, m/s |
| Uin | = | jet's inlet velocity, m/s |
| Uo | = | mean velocity, m/s |
| <v> | = | wall-normal velocity component, m/s |
| y+ | = | wall-normal direction [–] |
| δ** | = | shear-layer momentum thickness, m |
| φ | = | flow quantities |
| = | subgrid (unresolved) component | |
| μs | = | subgrid viscosity |
| ν | = | kinematic viscosity, m2/s |
| Γs | = | subgrid thermal diffusivity |
| Subscripts | = | |
| w | = | wall condition |
Nomenclature
| AN | = | amplitude of excitation |
| bij | = | Reynolds stress anisotropy tensor |
| D | = | jet's diameter, m |
| fo | = | most amplified frequency, Hz |
| fn/2 | = | frequency half of the preferred mode |
| f2n | = | frequency twice that of the preferred mode |
| H | = | jet's outlet-to-target-wall distance, m |
| II,III | = | second and third invariants |
| L(t) | = | integral length scale at inflow plane, m |
| Nu | = | Nusselt number [–] |
| <Nu>avg | = | Nu averaged till r/D = 6 |
| <Nu>stg | = | Nu at stagnation point |
| Pr | = | molecular Prandtl number [–] |
| Prs | = | subgrid turbulent Prandtl number [–] |
| qw | = | constant heat flux per area W/m2 |
| Re | = | Reynolds number of the jet [–] |
| = | Strouhal number based on shear-layer thickness [–] | |
| StD | = | Strouhal number based on jet's diameter [–] |
| T | = | temperature, K |
| To | = | jet inlet temperature, K |
| Tw | = | target wall temperature, K |
| <u> | = | radial velocity component, m/s |
| <ui> | = | mean axial velocity, m/s |
| = | velocity fluctuations, m/s | |
| uτ | = | shear velocity ( |
| Ub | = | time-averaged bulk velocity, m/s |
| Uin | = | jet's inlet velocity, m/s |
| Uo | = | mean velocity, m/s |
| <v> | = | wall-normal velocity component, m/s |
| y+ | = | wall-normal direction [–] |
| δ** | = | shear-layer momentum thickness, m |
| φ | = | flow quantities |
| = | subgrid (unresolved) component | |
| μs | = | subgrid viscosity |
| ν | = | kinematic viscosity, m2/s |
| Γs | = | subgrid thermal diffusivity |
| Subscripts | = | |
| w | = | wall condition |
Acknowledgments
The authors would like to thank Prof. Dr. M. Schäfer and Dr.-Ing. D. Sternel (Fachgebiet für Numerische Berechnungsverfahren im Maschinenbau (FNB), Technische Universität, Darmstadt, Germany) for providing the FASTEST code and helpful discussions.