A two-dimensional Hartmann wavefront sensor is used to measure the aero-optical effects when the optical beam passes through a low velocity heat turbulent jet. The wavefronts are reconstructed by the results of the measured wavefront gradient, and the wavefront aberration is obviously shown. The correlation function is obtained from angular beam-jitter measurements, and the convection velocity and turbulence scale size of the flowing turbulence jet are calculated. These results show that the Hartmann wavefront sensor is not only used to measure the aero-optical effects in turbulent medium, but also utilized to perform non-intrusive studies of fluid flows.