# Unsteady Volumetric Entropy Generation Rate in Laminar Boundary Layers

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## Abstract

**:**

## Introduction

## Experimental Facility and Data Reduction

_{θ}, Reynolds number based upon momentum thickness, values of 391 and 83 respectively. The corresponding free stream velocities were 17 and 3.5 meters per second respectively. The flow was laminar, as confirmed by the first turbulent spots being detected downstream of the measurement location using a single hot film sensor attached to the wall.

## Results and Discussion

**Figure 2.**Illustration of the potential variation in the velocity and entropy generation rate per unit volume with time in the near wall region for a laminar boundary layer subjected to 6% free stream turbulence.

**Figure 3.**(a) Maximum variation in velocity profiles and (b) entropy generation rates per unit volume across a laminar boundary layer subjected to free stream turbulence of 1.3%; Re

_{θ}= 391.

**Figure 4.**(a) Maximum variation in velocity profiles and (b) entropy generation rates per unit volume across a laminar boundary layer subjected to free stream turbulence of 6%; Re

_{θ}= 83.

## Conclusion

## Nomenclature

Re_{θ}=ρUeθ/μ | Reynolds number based on momentum thickness | |

S´´´ | Entropy generation rate per unit volume | Wm^{-3}K |

T | Absolute temperature | K |

u | Instanteous streamwise velocity | m s^{-1} |

U_{e} | Boundary layer edge velocity (0.99
U_{∞}) | m s^{-1} |

x | Stream-wise coordinate, distance from leading edge | m |

y | Cross-stream coordinate, distance from wall | m |

## Greek

δ | Boundary layer thickness | m |

μ | Dynamic viscosity | N s m^{-2} |

θ | Momentum thickness | m |

ρ | Density | Kg m^{-3} |

## Subscripts

()_{max} | Maximum value |

()_{wall} | Conditions at the wall for mean profiles |

## References

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**MDPI and ACS Style**

Walsh, E.J.; Hernon, D.
Unsteady Volumetric Entropy Generation Rate in Laminar Boundary Layers. *Entropy* **2006**, *8*, 25-30.
https://doi.org/10.3390/e8010025

**AMA Style**

Walsh EJ, Hernon D.
Unsteady Volumetric Entropy Generation Rate in Laminar Boundary Layers. *Entropy*. 2006; 8(1):25-30.
https://doi.org/10.3390/e8010025

**Chicago/Turabian Style**

Walsh, E. J., and D. Hernon.
2006. "Unsteady Volumetric Entropy Generation Rate in Laminar Boundary Layers" *Entropy* 8, no. 1: 25-30.
https://doi.org/10.3390/e8010025