Aiaa 2001-0447 Experimental Investigation of Separation on Low Pressure Turbine Blades

Measurements of the flow field around a low pressure turbine blade are presented. The purpose of the experimental study is to investigate the detailed transition and separation characteristics on low pressure turbine blades. The present study focuses on the effect of Reynolds number on the formation of separation bubbles on the turbine blade surface. Specific attention is paid to the flow within and around the region of separation. Experiments have been conducted using a turbine blade cascade in a tow tank and wind tunnel using DPIV and flow visualization, respectively. In the tow tank, a turning vane cascade model was constructed to validate the diagnostics for future wind tunnel tests. DPIV has been employed to measure the flow velocity near the surface of the blade with a wall-adaptive Lagrangian parcel tracking algorithm which enables the determination of velocities near surface boundaries. Since this technique is instantaneous, it allows investigation of unsteady flow phenomenon critical in understanding transient separation. Measurements are run for a Re range from 1 · 10 4 to 1 · 10 5 ; preliminary measurements are presented from 1 · 10 4 to 4 · 10 4. In the wind tunnel, a 6 blade cascade model was constructed with a variable exit angle for flow visualization and DPIV. Smoke wire visualization results are presented for Re 2.5 · 10 4 to 9 · 10 4. Nomenclature Re Reynolds number β Exit angle, deg Subscripts c Chord length SSL Suction surface length ∞ Freestream d Wire diameter Introduction The gas turbine engine has served as the predominant form of aerospace propulsion in the latter half of the 20th century and increasing performance requirements for gas turbine engines in military and commercial aerospace applications continue to drive development in specific components of gas turbine engines. Small improvements have been shown to result in significant cost savings in the past, particularly in off design operating conditions where separation becomes a significant factor in performance degradation such as in the low pressure turbine (LPT). Designed for high Re operating conditions near sea level, the low-pressure turbine section is prone to separation and transition effects at high altitude cruise where low air density results in a reduced Re. There are several parameters that must be studied in order to * Graduate student; member AIAA. develop a comprehensive understanding of the flow behavior around the low-pressure turbine blade, including Re, FSTI, blade geometry …