Experimental studies have been conducted on a modified T106 low pressure turbine (LPT) profile in an annular 1.5 stage axial turbine rig at the Chair of Thermal Turbomachines and Aeroengines, Ruhr-Universität Bochum. The rig setup allows the highly resolved measurement of unsteady wake–stator flow interaction in both space and time. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. In the present paper, an experimental approach to the investigation of unsteady phenomena is proposed. Time-averaged and instantaneous measurement data from 2D flow field traverses at the stator exit are provided for the analysis of the periodically unsteady vortex formation, displacement, and suppression. Additional time-accurate blade pressure data are used to study the relationship between the flow structures downstream of the stator row and the immediate intermittent wake impact on the blades. Bar wake kinematics is also discussed in relation to the observations.
The experimental results reported in this contribution address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile low-pressure turbine (LPT) stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, nonuniform, increasing pitch across the span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening, and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.
This paper transfers findings from linear cascade studies to the annular system. Experimental studies have been conducted on the newly designed 1.5 stage full annular rotating axial turbine rig at Chair of Thermal Turbomachinery, Ruhr-Universität Bochum. Therefore, an existing large scale low speed test rig was retrofitted with newly designed T106RUB low pressure turbine (LPT) blading, state-of-the-art measurement technologies and multi-dimensional traversing devices to allow for highly resolved measurements of unsteady wake stator flow interaction in both space and time. Incoming wakes are generated by a variable-speed driven rotor disk equipped with cylindrical bars.
The measuring concept for an in-depth analysis of unsteady flow phenomena is presented and results from highly resolved time-averaged and time-resolved flow field traverses are discussed and compared. In detail the time-dependent interaction of periodically passing bar wakes with the boundary layers and secondary flow structures of the T106RUB stator row is investigated. Special emphasis is put on time-varying dilatation and location of individual components of the vortex system and on potential flow separation along the blade suction surface. It is evaluated how these factors can contribute to a time-dependent homogenization of stator exit flow and a consequent loss reduction in the present configuration.
In this work, we present the results of the numerical investigations of periodic wake–secondary flow interaction carried out on a low pressure turbine (LPT) equipped with modified T106-profile blades. The numerical predictions obtained by means of unsteady Reynolds-averaged Navier–Stokes (URANS) simulations using a k-ω-model have been compared with measurements conducted in the same configuration and showed a good agreement. Based on the verified numerical data, the Q-criterion has been employed to characterize the secondary flow structures and accurately identify their origin. An analysis of the fundamental wake kinematics and the unsteady vortex migration revealed dominant interaction mechanisms such as the circumferential fluctuation of the pressure side horseshoe vortex (HSV) and its direct interaction with the passage vortex (PV) and the concentrated shed vortex (CSV). Finally, a correlation with the total pressure loss coefficient is provided and a link to the incoming wake structures is given.
In the proposed paper the transient interaction between periodic incoming wakes and the laminar separation bubble located on the rear suction surface of a typical, highly loaded LPT blade is investigated by means of highly resolved large-eddy simulations. An annular, large scale, 1.5-stage LPT test-rig, equipped with a modified T106 turbine blading and an upstream rotating vortex generator is considered and the numerical predictions are compared against hot film array measurements. In order to accurately assess both baseline transition and wake impact, simulations were conducted with unperturbed and periodically perturbed inflow conditions. Main mechanisms of transition and wake-boundary layer interaction are investigated utilizing a frequency-time domain analysis. Finally visualizations of the main flow structures and shear layer instabilities are provided utilizing the q-criterion as well as the finite-time Lyapunov exponent.
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