Abstract
The characteristic differences in the near wall turbulent structure and the shear stress pattern between a uniform flow and a wall jet with a co-flow stream over a flat surface have been numerically investigated in the present work. A uniform flow of free stream Reynolds number \(Re_{\infty } = 8.64 \times 10^{5}\) is considered to be flowing over a flat plate in one case. Separately, a wall jet with nozzle exit Reynolds number \(Re_{j} = 18000\) along with parallel co-flow stream of Reynolds no \(8.64 \times 10^{5}\) is assumed for the investigation. Realizable \(k - \varepsilon\) model with an enhanced wall treatment scheme has been implemented to capture the near wall features with more details and accuracy. Numerical study reveals that the introduction of turbulent wall jet along with uniform co-flow stream increases the wall shear stress noticeably. The near wall flow structures on introduction of wall jet completely differ from that of the uniform flow. The turbulent fluctuations and the resulting turbulent stress components are found comparatively much higher in case of wall jet.
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Abbreviations
- \(u_{\infty }\):
-
Free stream velocity [m/s]
- \(u_{j}\):
-
Jet velocity at nozzle exit [m/s]
- ρ:
-
Density of air [kg/m3]
- ν:
-
Fluid kinematic viscosity [m2/s]
- \(\mu\):
-
Fluid kinematic viscosity [m2 /s]
- w:
-
Nozzle slot thickness [m]
- \(\tau_{{{\text{wx}}}}\):
-
Wall shear stress at location x [Pa]
- \(y_{1/2}\):
-
Wall normal distance where the local stream-wise velocity (u) is half the maximum velocity [m]
- ym:
-
Wall normal distance where the local stream-wise velocity (u) is maximum. [m]
- \(\delta\):
-
Boundary layer thickness for the uniform flow over flat surface.[m]
- \(Re_{j} = \frac{{u_{j} L}}{\nu }\):
-
Jet exit Reynolds number
- \(Re_{\infty } = \frac{{u_{\infty } L}}{\nu }\):
-
Free stream Reynolds number based on plate length L
- \(C_{{{\text{fx}}}} = \frac{{2\tau_{{{\text{wx}}}} }}{{\rho u_{m}^{2} }}\):
-
Local skin friction coefficient
- \(\infty\):
-
Free stream
- j:
-
Jet
- wx:
-
Position along the wall
- m:
-
Maximum value
- t:
-
Turbulent
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Nath, P., Patari, A. (2024). The Differences in the Near Wall Turbulent Structure Between a Uniform Flow and a Wall Jet with Co-Flow—A Numerical Study. In: Singh, K.M., Dutta, S., Subudhi, S., Singh, N.K. (eds) Fluid Mechanics and Fluid Power, Volume 2. FMFP 2022. Lecture Notes in Mechanical Engineering. Springer, Singapore. https://doi.org/10.1007/978-981-99-5752-1_23
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DOI: https://doi.org/10.1007/978-981-99-5752-1_23
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