A prediction method for flow in axial compressors

[摘要] ENGLISH ABSTRACT: A procedure is presented for predicting the flow through axial compressors. The matrixthroughflow equation is transformed to yield an expression of radius dependent on streamfunction and axial position. The solution of the resultant equation combines the advantagesof following streamlines through the calculation domain (as in the streamline curvaturemethod, SCM) with the stability of the matrix throughflow method (MTFM), and iscorrespondingly called the streamline through flow method (STFM). The predictions of themethod were compared to analytical results for a number of inviscid test cases and gave good results.As with the SCM and MTFM, using STFM to predict turbomachinery flows requires empiricalmodels for cascade loss and deflection as well as endwall loss. The off-design loss anddeflection model of Howell was used as the basis for a new off-design correlation, H2, validfor axial velocity density ratios (AVDR) of unity. The H2 correlation was developed fromthe NACA 65-Series database as carpet-plotted by Felix.A simple subcritical Reynolds number correlation for loss and deflection was adapted froma method of Roberts, using inlet blade chord Reynolds number, camber angle, pitch-chordratio, maximum blade thickness-chord ratio and turbulance factor as parameters. The H2correlation together with the adapted Roberts correlation gave good predictions of loss anddeflection for low-Reynolds number cascade flows at AVDR values of unity.Measurements were taken at the compressor inlet and behind each blade row of a low speed,three stage axial flow compressor at three flowrates: near-design, near-surge and near-choke.The predictions of STFM using Howell's endwall loss models, the modified low Reynoldsnumber correlation and respectively Howell's original off design method and H2 werecompared with the experimental results. Howell's method predicted pressure rise to within3% at design and 10% at off-design, compared to 4% at design and 9% at off-design for theH2 method. The prediction of flow angles for H2 were considerably worse than that ofHowell. This was deemed to be caused by AVDR effects.An interim AVDR correlation, dependent on stagger angle, was used together with H2.Choosing values of AVDR for the interim correlation which together with H2 would predictflow angles to match the experimental values, predictions of total pressure rise within 3% atdesign and 8% at off-design were achieved. As a measure of confidence can be placed in H2and the modified low Reynolds number correlation, the endwall loss correlation of Howellwas determined to be the cause of lack of further gains in accuracy.

[发布机构] Stellenbosch University