A practical methodology to estimate bed shear stress in smooth wall-bounded turbulent flows using DNS data

The measurement of bed shear stress is incredibly challenging in the field as well as in the laboratory. Here, a practical method is presented to estimate the bed shear stress by appealing to the inner-outer layer coupling in conjunction with data obtained from high-Reynolds number Direct Numerical Simulations (DNS) of wall-bounded turbulent flows. The inner-outer layer coupling suggests that there exists a unique relationship between inner and outer length and time scales. The data from the DNS studies have been used to derive a relationship between bed shear stress and outer layer velocity scale. This relationship is then tested using experimental data of open channel flow in a laboratory setting and excellent agreement has been found. The new methodology simplifies the estimation of bed shear stress as the need of near boundary measurements has been obviated. This study also demonstrates the utility of DNS of turbulent flows for practical applications.