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A wind tunnel comprises means for confining the cross‐section of an electric are to increase its current density and temperature and for introducing a fluid into the are to form a hot plasma and means for increasing the velocity of the plasma and directing its flow uniformly over a supported model. In the illustration, water, gaseous or liquid air, or nitrogen, is introduced under pressure tangcntially into a chamber 20 so as to form a vortex around an are struck between electrodes 16, 17. The vortex confines the are and the resulting plasma is directed by a divergent duct 11 over a model 14 in a tunnel 13, preferably exhausted to 3 cm. pressure. The tunnel contains an observation window 23, and together with the model is movable relatively to the duct 11 by a joint formed between portions 25, 26 with scaling rings 28. Flow velocities of the order of 25,000 ft.sec. and temperatures of the order of 10,000 dcg. C. are stated to be attained.