Velocity and temperature scaling in a rough wall boundary layer

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.