Some experiments were made for the buoyant jet from a square orifice with a square disc placed on it in static ambient and concentration along the axis in self-similar area behind disc was measured. And at the same time a three-dimensional mathematical model was established to simulate the whole flowing under different conditions. All the results predicted by the numerical calculation were substantiated by the experiments. The results were compared with experiential formula for obstructed round buoyant vertical jets in static ambient and it was found that the two concentration distributions had good accordance. Star shape of temperature isolines on cross-sections in the near areas from the disc was found and it was a very special figure for obstructed square buoyant vertical jets with a square disc. The shape will transform to concentric circles gradually alike to the round buoyant vertical jet in self-similar area with increasing of the distance from the disc.

A three-dimensional eddy model considering buoyancy was established to simulate vertical buoyant flow from a square orifice in static ambient. The hybrid finite analytic method with stagged grid was used to solve this model. Results showed that axial velocities from a square orifice coincided well with those from a circular one after a little distance from the jet mouth. The shapes of vertical velocity distribution on different height cross-sections tallied well with those from a circular orifice. The existence of self-similar area of longitudinal velocity was confirmed also.