Abstract: The icing wind tunnel is the main facility for aircraft icing research. Water droplet diameter is one of the most important parameters of tests in an icing wind tunnel. Currently, the value of water droplet diameter is decided mainly by the test speed. To obtain the rule for selecting a reasonable droplet size, the formula for the selection of water droplet diameters in an icing wind tunnel test is derived in this article. Then the effect of speed on droplet size and test results is studied. Water droplet collection efficiency for different speeds and its corresponding droplet sizes on test models is computed with Eulerian method, which is then compared with the values on a full scale body. The result shows that, for small water droplets, when the reference speed is low, the ratio of the test speed to the reference speed should not be selected too small, and it should not be too large when the reference speed increases to a certain value. For large water droplets, when the reference speed is low, the ratio should not be selected too small either; however, when the reference speed increases to a certain value, the changes of test speeds and the corresponding droplet sizes do not affect the collection efficiency on the test model. The same collection efficiency on full scale bodies and test models can be obtained once the ratio of the test speed to the reference speed is in the range of 0.3 to 1.0.

Key words: aircraft icing, icing wind tunnel, icing scaling law, water droplet diameter, icing test