This paper presents experimental results on unsteady turbulent flow in a low-pressure turbine blade cascade, specifically exploring the effects of blade vibrations on wake topology and turbulence structure. The study focused on comparing the flow patterns of a stationary blade to those observed during its bending and torsion vibrations. Hot-wire anemometry was used for the experimental analysis. The flow velocity was characterized by a chord-based Reynolds number of approximately $R{e}_c\approx 2.3\times {10}^5$, with the excitation frequency set at $f=72.8\mathrm{Hz}$. The findings reveal a strong effect of the bending mode on the wake topology, resulting in a 5% reduction in the streamwise velocity deficit compared to the stationary and torsional modes. Additionally, the bending mode encourages the active formation of large vortices in the wake region, which leads to a fivefold increase in the integral length scale. In contrast, the Kolmogorov microscale remains consistent across all scenarios, exhibiting a minimum in the wake region and a maximum in the inter-blade space. The paper also discusses the impact of blade oscillations on the energy dissipation rate. Various calculation methods yield consistent results, indicating that the lowest dissipation rate occurs during the bending mode. Furthermore, the paper emphasizes the spectral analysis of turbulent flow and provides a comprehensive assessment of the Taylor microscale under different experimental censorious.

Modern efficient and robust steam turbines must be designed for large operating ranges and run at off-design conditions and high backpressures. Therefore, there is a danger that in some operating conditions, last-stage rotor blades can suffer from self-excited vibration (flutter), leading to severe failures of rotor blades or turbine units. In order to avoid this, the design of aerodynamically stable last stage rotor blades became a major topic for all steam turbine manufacturers and a validated numerical model for flutter prediction during the blade preliminary design phase is required. As flutter measurement is impossible in real turbines, controlled flutter tests on simplified experimental models must be used. However, experimental flutter testing facilities are rare. This paper reports on a flutter test rig enhancement to transonic flow and numerical data validation of aerodynamic stability in a linear turbine blade cascade. Aerodynamic forces and moments are estimated for different boundary conditions at pure bending, pure torsion and combined modes. The results are compared to numerical simulations performed using commercial code ANSYS CFX. Good agreement between the experiment and the numerical simulations proved a successful validation of the numerical tool.

This paper investigates the oscillatory effect of a single blade on the turbulence wake downstream of a low-pressure turbine cascade. Experimental investigations were conducted at a chord-based Reynolds number of $2.3\times {10}^5$ with an excitation frequency of 73 Hz. The experimental campaign encompassed two incidence angles (−3° and +6°) and three blade motion conditions: stationary, bending, and torsional vibrations. Turbulence characteristics were analyzed using hot-wire anemometry. The results indicate that the bending mode notably alters the wake topology, causing a 5% decline in streamwise velocity deficit compared to other modes. Additionally, the bending motion promotes the formation of large-scale coherent vortices within the wake, increasing the integral length scale by 7.5 times. In contrast, Kolmogorov’s microscale stays mostly unaffected by blade oscillations. However, increasing the incidence angle causes the smallest eddies in the inter-blade region to grow three times larger. Moreover, the data indicate that at −3°, bending-mode results in an approximate 13% reduction in the turbulence energy dissipation rate compared to the stationary configuration. Furthermore, the study emphasizes the spectral features of turbulent flow and provides a detailed assessment of the Taylor microscale under different experimental conditions.

Experimental flutter testing of high-aspect ratio rotor blades is a mainstay of turbomachinery research. However, rotor blades are never identical, and geometrical errors between actual and nominal geometries exist due to limited machining precision or assembly imperfection. The paper presents the initial phase of the controlled flutter research of a linear turbine blade cascade with a geometric deviation in one blade position. A subsonic wind tunnel with four flexibly mounted blades in an otherwise rigid blade cascade is employed at one angle of incidence and three low reduced frequencies. Measurements are performed with an angular position deviation (±1.5°) of one blade in pure bending and torsion modes. A tangible effect of one blade’s slight incidence angle offset on the vibrating blade cascade aerodynamic stability is demonstrated, and this research effort opens the door to a more extensive testing campaign.