In this study, the analysis of the turbulent flow separation on the wall of the main conduit in a pipe fitting with branching angleθ
p of 135° is presented. The flow in the pipe fitting is analyzed by the free-streamline theory. Then the separation point of the turbulent flow is analyzed using the boundary layer theory. The calculated results indicate that the separation point χ
s/h
1 (h
1 denotes the upstream section of the main conduit.) depends on the area ratio m, the length of the upstream section of the main conduit l
1d/h
1, the Reynolds number Re
1r and the ratio of lateral discharge to total discharge Q
2/Q
1. Also, the experiments were made on the same conditions for the analysis. The experimental reseults show that χ
s/h
1 is dependent on m and Q
2/Q
1. When l
1d/h
1 and Re
1r are large enough, the values of χ
s/h
1 obtained by the experiment indicate that the same tendency as the calculated ones. But the values of χ
s/h
1 obtained by experiment are usually smaller than those obtained by the calculation. Therefore, the separation point of the real flow exists farther upstream than that of the calculation.
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