Effect of non-collimated light path on flow field's temperature reconstruction by moiré tomography

•The effect of non-collimated light on flow field's temperature diagnosis by moiré tomography is verified.•It is found that the fringes will tilt to the right and the temperature will increase when the little lens moves to the left.•The fringes will tilt to the left and the temperature will decrease when the little lens moves to the right. In this paper, the effect of non-collimated light path on flow field's parameter diagnosis by moiré tomography is discussed, and a candle combustion flow field is chosen for experiment. To obtain the non-collimated light path, a little lens which is used for beam expanding and collimation is equidistantly moved twice to the left (near the light source) and right (away from the light source) on the basis of the collimated position. Therefore, for a certain cross section, five sets of moiré fringes can be obtained from experiment for further analysis and discussion. And, three cross sections of the measured candle combustion are chosen for practical discussion. The results manifest that the moiré fringes are tilt to the right when the little lens moves to the left, and the temperature is larger than that of obtained by the collimated light path. Meanwhile, it is found that the moiré fringes are tilt to the left when the little lens moves to the right, and the temperature is smaller than that of obtained by the collimated light path. Finally, the possible factors which could affect the measurement accuracy of OCT methods for diagnosing flow fields are discussed.