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Velocity and temperature scaling in a rough wall boundary layer
1Department of Mechanical Engineering, University of Newcastle, New South Wales 2308, Australia.
Summary
This study analyzed turbulent boundary layers with rough surfaces, measuring velocity and temperature fluctuations. Findings reveal distinct spectral slopes and structure function behaviors, offering insights into turbulent flow dynamics.
Area of Science:
- Fluid dynamics
- Turbulence research
- Heat transfer
Background:
- Turbulent boundary layers are crucial in many engineering applications.
- Understanding flow behavior over rough surfaces is essential for accurate modeling.
- Previous studies have explored spectral properties but lacked detailed analysis across rough surfaces.
Purpose of the Study:
- To investigate the effects of regularly spaced cylindrical roughness elements on turbulent boundary layer characteristics.
- To quantify spectral and cospectral properties of velocity and temperature fluctuations.
- To analyze the behavior of structure functions and scaling/intermittency exponents.
Main Methods:
- Experimental measurements of velocity (u, v, w) and temperature (θ) fluctuations.
- Analysis of power spectral densities and cospectra.
- Estimation of structure functions and scaling/intermittency exponents.
Main Results:
- Spectra of u and v fluctuations showed distinct slopes, with u having the largest and v the smallest.
- The temperature fluctuation spectrum closely matched the mean turbulent energy spectrum.
- Cospectra slopes (uθ > uv > vθ) and structure function behaviors were consistent with spectral findings.
- Scaling exponents decreased towards the wall, while intermittency exponents increased.
Conclusions:
- The study provides detailed insights into turbulent flow physics over specific rough surfaces.
- Observed spectral and structural behaviors offer valuable data for validating turbulence models.
- The findings highlight the influence of surface roughness on turbulent transport and energy dissipation.
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