Numerical investigation of the combined effect of swirler and primary jets on the recirculation zone of a can‐type combustor by means of an orthogonal array technique

An orthogonal array technique is used in the present work to investigate, numerically, the effects of the swirler and the primary jets on the characteristics of the recirculation zone of a can‐type gas turbine combustor. The computer code used for this purpose is first validated with the available experimental data. The effects of change in the percentage flow rate through the swirler, the swirl number, the hub diameter of the swirler and the diameter of the primary injection holes (which influences the velocity of the jets) are estimated first. It is found that the flow rate through the swirler and the size of the primary injection hole have much more influence on the characteristics of the recirculation zone than the swirl number and the hub diameter of the swirler. But the earlier studies show that for a given flow rate through the swirler, the swirl number and swirler geometry have considerable influence on the characteristics of the recirculation zone in the absence of primary jets. Therefore it is inferred that there may be a critical point, based on the ratio of flow rate through the swirler to that of primary holes, beyond which the effects of swirl number and the swirler geometry dominate the effect of primary jets in determining the characteristics of the recirculation zone. This critical point is determined by gradually reducing the flow through the primary holes. It is found that, initially, the recirculation ratio (ratio of the mass of fluid recirculated to that sum of the mass flow rate through the swirler and through that of primary hole) reduces because of weakening of the primary jets but after the critical point it increases because of the swirler effect taking over the role of providing the recirculation. It is also observerd that the length of the recirculation zone increases as the strength of the primary jets reduces.