X-Wire response in turbulent flows of high-intensity turbulence and low mean velocities

The angular response of an x-wire is studied at low velocities (0.25-1.4 m/s). It is found that the k-factor in the modified cosine law is strongly velocity-dependent. The implications of this for multicomponent measurement are explored, and a practical scheme for incorporating it is proposed. At lower velocities a total loss of direction sensitivity is observed that leads to additional errors in x-wire measurements. Expressions are derived for evaluating when cross-flow errors begin to affect x-wires. Also, a "dropout" phenomenon is observed in which certain voltage pairs from an x-wire cannot be converted into the velocity components. The implication of this dropout on the turbulence measurements is also discussed.