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Characteristics of Transitional Separation Bubble Formed Over Negatively and Positively Skewed Anisotropic Rough Surface

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Fluid Mechanics and Fluid Power, Volume 2 (FMFP 2022)

Part of the book series: Lecture Notes in Mechanical Engineering ((LNME))

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Abstract

Effect of leading-edge anisotropic erosion (negative skewness) and deposition (positive skewness) on a transitional separation bubble (TSB) is investigated using single-wire hot wire anemometer for a Reynolds number (Rec) of \(2.5 \times 10^{5}\), , based on the model chord and tunnel free stream velocity. Three different models are fabricated for investigation, whose surfaces are smooth (SS), sand blasted (BS) and sand deposited (DS), respectively. The fabricated rough surfaces are three-dimensionally irregular and replicate the anisotropic pattern of an operationally deteriorated turbine blade due to chronic exposure to harsh working environments. Results of positive and negative skewed rough surfaces are compared with that of smooth surface. The bubble is observed to be shortened by about 35% and 10% of that formed over SS for DS and BS, respectively. Premature transition is observed on DS, which is 49% earlier than BS case. Though the transition point varies, it is interesting to note that the chord length occupied by the transition and turbulent region of the bubble is almost same for all the cases. Presumably, more than the negatively skewed anisotropic rough surface, the positive counterpart tends to influence the boundary layer stability and thereby the transition characteristic of separation bubble.

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Abbreviations

c:

Chord length of flat plate model [mm]

D:

Leading-edge diameter of the flat plate model [mm]

\(H_{12}\):

Boundary layer shape factor

\({\text{Re}}_{c}\):

Reynolds number based on the chord of the flat plate model

\({\text{Re}}_{{\delta_{2,S} }}\):

Reynolds number based on momentum thickness at separation

\({\text{Re}}_{{l_{1} }}\):

Transitional Reynolds number (based on transitional length of TSB)

\(l_{b}\):

Mean length of TSB [mm]

\(l_{0}\):

Length of laminar portion of TSB [mm]

\(l_{1}\):

Length of transitional portion of TSB [mm]

\(l_{2}\):

Length of turbulent portion of TSB [mm]

\(\overline{u}\):

Streamwise mean velocity [m/s]

\(U_{e}\):

Boundary layer edge velocity [m/s]

\(u_{{{\text{rms}}}}\):

Root-mean-squared fluctuation of streamwise velocity [m/s]

\(u_{{{\text{rms}}_{{{\text{max}}}} }}\):

Maximum of local rms fluctuation of streamwise velocity [m/s]

\(x_{T^{\prime}}\):

Streamwise location of onset of transition [mm]

\(x_{T}\):

Streamwise location of end of transition (or) point of transition [mm]

\(x_{R}\):

Streamwise location of reattachment [mm]

\(\gamma\):

Separation angle [o]

\(\delta_{1}\):

Displacement thickness of boundary layer [mm]

\(\delta_{2}\):

Momentum thickness of boundary layer [mm]

\(\delta_{{1_{t} }} /\delta_{{2_{s} }}\):

Proximity parameter (Displacement thickness at transition/Momentum thickness at separation)

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Acknowledgements

The present work is part of the research project funded by DST-SERB, New Delhi (File No.: EMR/2016/005834). Also, the resources offered by SASTRA management is sincerely acknowledged.

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Authors and Affiliations

  1. School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, 613401, India

    K. T. Ganesh & K. Anand

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  1. K. T. Ganesh
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  2. K. Anand
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Correspondence to K. Anand .

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Editors and Affiliations

  1. Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India

    Krishna Mohan Singh

  2. Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India

    Sushanta Dutta

  3. Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India

    Sudhakar Subudhi

  4. Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India

    Nikhil Kumar Singh

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Ganesh, K.T., Anand, K. (2024). Characteristics of Transitional Separation Bubble Formed Over Negatively and Positively Skewed Anisotropic Rough Surface. 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_8

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  • DOI: https://doi.org/10.1007/978-981-99-5752-1_8

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