Fig. 1. Optical testing system

Fig. 2. Temperature contour of Y=0 cross-section in the vertical direction

Fig. 3. Temperature distribution in the vertical direction in front of the φ940 mm mirror

Fig. 4. Distributions of 25 sampling points on the circular section

Fig. 5. Variation of wind speed with distance

Fig. 6. Temperature contours with 4 fans on one and both sides

Fig. 7. Effects of the different angle on temperature and optical path difference

Fig. 8. Illustration of 4 fans on both sides with the tilt angle 15°

Fig. 9. Effects of the different numbers on temperature and optical path difference

Fig. 10. Temperature contours of three cross-sections with different numbers of fans

Fig. 11. 0° astigmatism coefficients before and after forced convection

Fig. 12. Deformation contours before and after forced convection