Side-projected dual-fiber velocity sensors with various fiber core sep
arations for in vivo measurements were developed and tested. Good line
arity between the flow velocity and the Doppler shift frequency is obt
ained with this sensor in both the forward (toward the sensor tip) and
reverse (away from the sensor tip) flow directions, Experimental and
numerical analysis of the data showed that the boundary layer along th
e side wall of the fiber sensor varies with the flow velocity.