![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
Direct numerical simulation (DNS), two shear-stress transport (SST) turbulence models, and three k-ε models are used to predict mixed convection associated with air in cross flow over an isothermal, finned cylinder. The DNS predictions reveal complex time-variation in the flow field. Convection heat transfer coefficients predicted by the SST models are in good agreement with those generated by DNS, whereas the k-ε models do not accurately predict heat fluxes. Correlation-based predictions of heat transfer coefficients are, in general, in poor agreement with the DNS and SST predictions. The impact of various geometrical modifications on convection coefficients is also presented.
Nomenclature
| A | = | area (m2) |
| C1ε, C2ε, C3ε | = | κ-ε model constants |
| = | κ-ε model constants | |
| D | = | diameter of cylinder (m) |
| Eγ1, Eγ2 | = | SST transitional production term (kg/ m s3) |
| F1, F2 | = | SST blending functions |
| g | = | gravitational acceleration (m/s2) |
| Gr | = | Grashof number |
| h | = | convection coefficient (W/m2 K) |
| H | = | height (m) |
| k | = | thermal conductivity (W/m K) |
| L | = | length (m) |
| n | = | surface normal |
| p | = | pressure (Pa) |
| Pκ, Pb | = | SST and κ-ε production terms (kg/ m s3) |
| Pγ1, Pγ2, Pθt | = | SST transitional production term (kg/ m s3) |
| q″ | = | heat flux (W/m2) |
| Re | = | Reynolds number |
| = | transitional momentum thickness Reynolds number | |
| r, z, θ | = | coordinate directions |
| s | = | separation distance (m) |
| S | = | fin pitch (m), turbulent strain rate (s−1) |
| t | = | time (s), thickness (m) |
| T | = | temperature (°C) |
| u | = | velocity (m/s) |
| V | = | average air velocity (m/s) |
| W | = | width (m) |
| x, y, z | = | coordinate directions |
| α | = | thermal diffusivity (m2/s) |
| α1, β1, β2 | = | SST model constants |
| β | = | thermal expansion coefficient (K−1) |
| ε | = | specific rate of turbulence dissipation (s−1) |
| γ | = | turbulence intermittency |
| θ | = | reduced temperature T - T∞ (°C), angular direction |
| κ | = | turbulent kinetic energy (m2/s2) |
| µ | = | dynamic viscosity (kg/m s) |
| ν | = | kinematic viscosity (m2/s) |
| ρ | = | density (kg/m3) |
| σκ, σω, σω2 | = | SST model constants |
| σf, σθt | = | SST transitional model constants |
| σκ, σε | = | κ-ε model constants |
| T | = | normalized time (s) |
| ω | = | specific rate of turbulence dissipation (s−1) |
| Subscripts | = | |
| 0 | = | reference |
| ch | = | channel |
| cyl | = | cylinder |
| f | = | fin |
| surf | = | surface |
| tot | = | total |
| turb | = | turbulent |
| x, y, z | = | coordinate directions |
| ∞ | = | inlet |
| Superscripts | = | |
| – | = | average |
Nomenclature
| A | = | area (m2) |
| C1ε, C2ε, C3ε | = | κ-ε model constants |
| = | κ-ε model constants | |
| D | = | diameter of cylinder (m) |
| Eγ1, Eγ2 | = | SST transitional production term (kg/ m s3) |
| F1, F2 | = | SST blending functions |
| g | = | gravitational acceleration (m/s2) |
| Gr | = | Grashof number |
| h | = | convection coefficient (W/m2 K) |
| H | = | height (m) |
| k | = | thermal conductivity (W/m K) |
| L | = | length (m) |
| n | = | surface normal |
| p | = | pressure (Pa) |
| Pκ, Pb | = | SST and κ-ε production terms (kg/ m s3) |
| Pγ1, Pγ2, Pθt | = | SST transitional production term (kg/ m s3) |
| q″ | = | heat flux (W/m2) |
| Re | = | Reynolds number |
| = | transitional momentum thickness Reynolds number | |
| r, z, θ | = | coordinate directions |
| s | = | separation distance (m) |
| S | = | fin pitch (m), turbulent strain rate (s−1) |
| t | = | time (s), thickness (m) |
| T | = | temperature (°C) |
| u | = | velocity (m/s) |
| V | = | average air velocity (m/s) |
| W | = | width (m) |
| x, y, z | = | coordinate directions |
| α | = | thermal diffusivity (m2/s) |
| α1, β1, β2 | = | SST model constants |
| β | = | thermal expansion coefficient (K−1) |
| ε | = | specific rate of turbulence dissipation (s−1) |
| γ | = | turbulence intermittency |
| θ | = | reduced temperature T - T∞ (°C), angular direction |
| κ | = | turbulent kinetic energy (m2/s2) |
| µ | = | dynamic viscosity (kg/m s) |
| ν | = | kinematic viscosity (m2/s) |
| ρ | = | density (kg/m3) |
| σκ, σω, σω2 | = | SST model constants |
| σf, σθt | = | SST transitional model constants |
| σκ, σε | = | κ-ε model constants |
| T | = | normalized time (s) |
| ω | = | specific rate of turbulence dissipation (s−1) |
| Subscripts | = | |
| 0 | = | reference |
| ch | = | channel |
| cyl | = | cylinder |
| f | = | fin |
| surf | = | surface |
| tot | = | total |
| turb | = | turbulent |
| x, y, z | = | coordinate directions |
| ∞ | = | inlet |
| Superscripts | = | |
| – | = | average |