This paper presents an investigation of extracting air from the compressor discharge of a heavy-frame gas turbine. The study was aimed to verify results of an approximate analysis: whether extracting air from the turbine wrapper would create unacceptable nonuniformity in the flow field inside the compressor discharge casing. A combined experimental and computational approach was undertaken. Cold flow experiments were conducted in an approximately one-third scale model of a heavy-frame gas turbine; a closely approximated 3-D computational fluid dynamic analysis was also performed. This study substantiated the earlier prediction that extracting air from the turbine wrapper would be undesirable although this method of air extraction is simple to retrofit. Prediffuser inlet is suggested as an alternate location for extracting air. The results show that not only the problem of flow non-uniformity was alleviated with this alternate scheme, but the frictional power loss in the compressor discharge casing was also reduced by a factor of two.

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