Abstract: The Northwestern Polytechnical University 10 by 30 cm. transonic airfoil wind tunnel was converted from the 30 by 30 cm. supersonic wind tunnel in 1976. This facility is a two-dimensional tunnel with parallel sidewalls and top and bottom slotted walls which operates on direct blowdown from a supply of dry air. On each sidewall, there is a turnable disk at the region occupied by the model. Various open-area-ratios may be obtained by sealing some slots of the slotted walls. The tunnel is capable of operating at Mach number from 0.4 to 1.0 with corresponding Reynolds number range of 3×106 to 6×106 based on a 10 cm chord. Empty tunnel calibrations show that the local Mach number distribution obtained from wall static pressure varies less than ±0.005 from the average value in the test region occupied by the model.Surface pressure distributions on three RAE-104 section models with 5 cm., 10 cm. and 12.5 cm. chords respectively were measured in conditions of zero angle of attack: the Mach number range of about 0.4 to 0.8 and several open-area-ratios. Results of measurements show that when the value of open-area-ratio is 0.02 and the corresponding wind tunnel parameter T equals 0.64, the blockage interference practically vanishes.Comparisons between surface pressure distributions of RAE-104 section models which were obtained under three conditions of sidewalls show that;1.The lift coefficients obtained under conditions of porous turnable disk without local sidewall suction are much less than those obtained under conditions of free interference.2.The lift coefficients obtained under conditions of the solid turnable disk closely approach those under conditions of free interference, when the Mach number is less than 0.7.3.It is found that under the conditions of larger Mach numbers and angles of attack the turnable disk with local sidewall suction is the best one in the three.The comparison between results in this facility and those in the British National Physical Laboratory 20 by 8 inch transonic tunnel is presented.