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ABSTRACT
Improved understanding of the impact of the operating conditions on the heat transfer and fluid flow behaviors of an outlet guide vane (OGV) is essential for accurate prediction of the lifetime of jet engines. In this article, the heat transfer characteristics of an OGV at various Reynolds numbers (Re), free stream turbulence levels, Mach number (Ma), and surface roughness are studied numerically. The Re is kept at 300,000 and 450,000, respectively, the free stream turbulence intensity ranges from 3.2% to 13%, and the turbulent length scale is varied from 1.2 to 11 mm. The Ma is selected as 0.06, 0.25, and 0.35, and the sandy grain roughness height is increased from the smooth wall level up to 160 µm. Mid-span pressure coefficient and Nu distributions are presented. Basically, the heat transfer patterns and pressure profiles are weak functions of the Re and Ma. Increasing the Re slightly moves the transition position upstream, while the Ma has no effect on the transition process. On the suction side, the transition is induced by flow separation and a bump is visible in the pressure profile. However, the turbulence intensity, turbulence length scale, and surface roughness levels have significant effects on the heat transfer and pressure distributions. On the suction side, the bump is invisible and the “separation-induced transition” is replaced by the “by pass transition”. It is also found that the transition position moves upstream as the turbulence intensity, length scale, and roughness level increase.
Nomenclature
| Cp | = | pressure coefficient |
| cp | = | apecific heat |
| Flength | = | function to control transition length |
| Fonset | = | function to control transition onset location |
| h | = | heat transfer coefficient |
| k | = | turbulent kinetic energy |
| kr | = | geometric roughness height |
| ks | = | equivalent sand grain roughness height |
| = | non-dimensional equivalent sand grain roughness height ksuτ/ν | |
| L | = | vane axial chord length |
| Lu | = | turbulence integral length scale |
| Lx | = | CFD turbulent length scale |
| Ma | = | Mach number |
| Nu | = | Nusselt number |
| P | = | pressure |
| Prt | = | Prandtl number |
| Ps | = | static pressure on the vane |
| Psin | = | static pressure of the inlet flow |
| q | = | heat flux |
| Ra | = | centerline average roughness height |
| Re | = | Reynolds number |
| Reθ | = | momentum thickness Reynolds number |
| Reθc | = | critical Reynolds number where the intermittency first starts to increase |
| = | transition Reynolds number | |
| Reθt,rou | = | the transition onset for rough surface |
| S | = | strain rate magnitude |
| T | = | temperature |
| Tg | = | inlet gas temperature |
| Tu | = | turbulence intensity |
| Tw | = | wall temperature |
| U | = | velocity |
| uτ | = | friction velocity |
| u+ | = | the near-wall dimensionless velocity |
| U0 | = | inlet axial velocity |
| vt | = | eddy-viscosity |
| X | = | axial direction |
| Y | = | wall-normal distance |
| y+ | = | dimensionless distance from the wall |
| = | incidence angle of the OGV | |
| γ | = | intermittency |
| γeff | = | separation-induced transition coefficient |
| = | Von Karman constant | |
| Λ | = | thermal conductivity |
| = | dynamic viscosity | |
| μt | = | turbulent viscosity |
| = | kinematic viscosity | |
| = | density of air | |
| Ω | = | specific turbulent dissipation rate |
| Ω | = | magnitude of vorticity rate |
| Abbreviations | = | |
| CFD | = | computational fluid dynamics |
| OGV | = | outlet guide vane |
Nomenclature
| Cp | = | pressure coefficient |
| cp | = | apecific heat |
| Flength | = | function to control transition length |
| Fonset | = | function to control transition onset location |
| h | = | heat transfer coefficient |
| k | = | turbulent kinetic energy |
| kr | = | geometric roughness height |
| ks | = | equivalent sand grain roughness height |
| = | non-dimensional equivalent sand grain roughness height ksuτ/ν | |
| L | = | vane axial chord length |
| Lu | = | turbulence integral length scale |
| Lx | = | CFD turbulent length scale |
| Ma | = | Mach number |
| Nu | = | Nusselt number |
| P | = | pressure |
| Prt | = | Prandtl number |
| Ps | = | static pressure on the vane |
| Psin | = | static pressure of the inlet flow |
| q | = | heat flux |
| Ra | = | centerline average roughness height |
| Re | = | Reynolds number |
| Reθ | = | momentum thickness Reynolds number |
| Reθc | = | critical Reynolds number where the intermittency first starts to increase |
| = | transition Reynolds number | |
| Reθt,rou | = | the transition onset for rough surface |
| S | = | strain rate magnitude |
| T | = | temperature |
| Tg | = | inlet gas temperature |
| Tu | = | turbulence intensity |
| Tw | = | wall temperature |
| U | = | velocity |
| uτ | = | friction velocity |
| u+ | = | the near-wall dimensionless velocity |
| U0 | = | inlet axial velocity |
| vt | = | eddy-viscosity |
| X | = | axial direction |
| Y | = | wall-normal distance |
| y+ | = | dimensionless distance from the wall |
| = | incidence angle of the OGV | |
| γ | = | intermittency |
| γeff | = | separation-induced transition coefficient |
| = | Von Karman constant | |
| Λ | = | thermal conductivity |
| = | dynamic viscosity | |
| μt | = | turbulent viscosity |
| = | kinematic viscosity | |
| = | density of air | |
| Ω | = | specific turbulent dissipation rate |
| Ω | = | magnitude of vorticity rate |
| Abbreviations | = | |
| CFD | = | computational fluid dynamics |
| OGV | = | outlet guide vane |
Acknowledgment
The authors acknowledge the financial support provided by the Swedish Energy Agency, the Natural Science Foundation of China (No. 51206034), and the China Scholarship Council (CSC). In addition, GKN Aerospace provided the geometry model of the OGV.