Experimental Flow Analysis in a Modern Turbine Rear Structure with 3D Polygonal Shroud Under Realistic Flow Conditions

Continuous advancement of the existing design of turbine rear structure (TRS) leads to new challenges in terms of aerodynamic efficiency. This work presents experimental aero studies of the effect of the 3D polygonal shroud in the TRS comprising several types of guide vanes representative of a modern TRS: regular vanes, thickened vanes, and vanes with a mount bump. The experiments were performed in an engine-realistic facility for a fixed Reynolds number, 350000, and three operation points based on a low-pressure turbine (LPT) exit swirl angle. The current study shows that the thickened vane handles the on-design and off-design conditions with good aerodynamic performance. It is observed that a shroud bump significantly affects the pressure losses because of the additional vorticity region created from the bump itself, and it has an upstream influence on the outlet flow from the LPT.Disclaimer:\ua0The content of this article reflects only the authors’ view. The Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains

Experimental and numerical investigation of hydro power generator ventilation

Improvements in ventilation and cooling offer means to run hydro power generators at higher power output and at varying operating conditions. The electromagnetic, frictional and windage losses generate heat. The heat is removed by an air flow that is driven by fans and/or the rotor itself. The air flow goes through ventilation channels in the stator, to limit the electrical insulation temperatures. The temperature should be kept limited and uniform in both time and space, avoiding thermal stresses and hot-spots. For that purpose it is important that the flow of cooling air is distributed uniformly, and that flow separation and recirculation are minimized. Improvements of the air flow properties also lead to an improvement of the overall efficiency of the machine. A significant part of the windage losses occurs at the entrance of the stator ventilation channels, where the air flow turns abruptly from tangential to radial. The present work focuses exclusively on the air flow inside a generator model, and in particular on the flow inside the stator channels. The generator model design of the present work is based on a real generator that was previously studied. The model is manufactured taking into consideration the needs of both the experimental and numerical methodologies. Computational Fluid Dynamics (CFD) results have been used in the process of designing the experimental set-up. The rotor and stator are manufactured using rapid-prototyping and plexi-glass, yielding a high geometrical accuracy, and optical experimental access. A special inlet section is designed for accurate air flow rate and inlet velocity profile measurements. The experimental measurements include Particle Image Velocimetry (PIV) and total pressure measurements inside the generator. The CFD simulations are performed based on the OpenFOAM CFD toolbox, and the steady-state frozen rotor approach. Specific studies are performed, on the effect of adding “pick-up” to spacers, and the effects of the inlet fan blades on the flow rate through the model. The CFD results capture the experimental flow details to a reasonable level of accuracy

Infrared Thermography Investigation of Heat Transfer on Outlet Guide Vanes in a Turbine Rear Structure

Aerothermal heat transfer measurements in fluid dynamics have a relatively high acceptance of uncertainty due to the intricate nature of the experiments. The large velocity and pressure gradients present in turbomachinery application add further complexity to the measurement procedure. Recent method and manufacturing development has addressed some of the primary sources of uncertainty in these heat transfer measurements. However, new methods have so far not been applied in a holistic approach for heat transfer studies. This gap is bridged in the present study where a cost-effective and highly accurate method for heat transfer measurements is implemented, utilising infrared thermography technique (IRT) for surface temperature measurement. Novel heat transfer results are obtained for the turbine rear sturcture (TRS), at engine representative conditions for three different outlet guide vane (OGV) blade loading and at Reynolds Number of 235000. In addition to that, an extensive description of the implementation and error mitigation is presented

Analysis of Pressure Drop Data in Channel Flows Over Foul-Control Coatings

The two-dimensional channel flow is of great interest for experimental as well as numerical studies. From the experimental perspective test in channel equipment is preferred, because it is simple, practical and offers a favorable economic running cost. Especially with the growing interest in marine coating research, it is critical that coating testing equipment delivers realistic flow conditions, is simple to cut the experimental time and effort and yet accurate. In this sense, the flow channel facility offers more advantages than classical cases for experimental investigations. Whereas from the numerical investigations point of view, channel flow exhibits favorable boundary conditions to save computational effort, while providing a deep insight into details of the flow structures. An initiative is taken at Chalmers university to develop the channel flow (or a flowcell) experimental facility to cater for the need of studies on coatings. Therefore, the current paper, in the first step, describes the design and manufacture of the flowcell. Secondly, it presents the thoroughly conducted verification study of the smooth reference test section to demonstrate that experimental facility holds the measurement expectations. Subsequently, skin friction data for selected foul control coatings obtained from the pressure drop measurements in the flowcell are presented

Fluxes in a full-flooded lubricated Tapered Roller Bearing: Particle Image Velocimetry measurements and Computational Fluid Dynamics simulations

The acquisition of complex fluxes inside a Tapered Roller Bearing (TRB) via Particle Image Velocimetry (PIV) is an experimental challenge. This can be successfully performed by exploiting a special test rig having the outer ring manufactured with sapphire. In the present paper, the velocity field in the region between cage, rollers and outer race have been captured via PIV in a fully flooded lubricated TRB. The experimental conditions have been reproduced numerically via Computational Fluid Dynamics (CFD). The comparison of PIV results with CFD ones showed excellent consistency. It has been observed that, in the target domain, the tangential velocity of the lubricant is greater than those of the cage. In addition, in the proximity of the edges of the rollers, squeezing effects due to high gradients of pressure have been recorded. The distribution of flow rates due to the pumping effect in different regions of the TRB have been estimated

DIC for Surface Motion Analysis Applied to Displacement of a Stent Graft for Abdominal Aortic Repair in a Pulsating Flow

Stent graft migration has been recognized to influence the long-term durability of endovascular aortic repair. Flow-induced displacement forces acting on the attachment zones may contribute to this migration. An experimental perfusion model consisting of the flow loop described by Roos et al. 2014 was used for further characterization of the pulsating flow induced stent graft movements with monocular and stereoscopic configurations of an optical imaging system. This paper adds new information on displacement measurement accuracy and 3D deformation analysis of the stent graft, which is used for abdominal aortic aneurysm treatment. The work describes used modification of Soloff’s Stereo PIV reconstruction algorithm for surface motion analysis. It was found that the oscillation of the stent graft’s body in the perpendicular direction to the front plane was 5 times less than side movements of the bent stent graft. These results can be used for further studies on different stent graft geometrical configurations and CFD simulations using fluid-structure interaction approach

Experimental study on the low-pressure turbine wake interaction and development in the turbine rear structure

The aerodynamic characteristics of advanced turbine rear structures (TRSs) could be affected by the interaction between unsteady flow developed from low-pressure turbine (LPT) and outlet guide vanes (OGVs). Consequently, analyzing the details of the interactions between the rotor wakes, stator wakes and OGVs is essential to enhance the aerodynamic efficiency of the modern TRS. This paper presents time resolved flow field measurements in the TRS at engine representative flow conditions. Experiments were performed in an annular large-scale 1.5 stage turbine facility at Chalmers University of Technology, Laboratory of Fluid and Thermal Sciences. The facility provides engine-realistic boundary conditions for the TRS and experimental data were acquired using 5-hole and 7-hole probes (5HP and 7HP), hot-wire anemometry (HW) and Particle Image Velocimetry (PIV). The PIV and HW measurements were conducted for the first time to enhance the understanding of unsteady flow phenomena and to investigate the development of TRS inflow structures. The observed unsteady interaction mechanism between the rotor wakes, stator wakes and OGV is of prime interest and investigated in detail. The breakdown of rotor and stator wakes through the TRS are documented and the OGV wake is analysed in detail by PIV

Projects in Applied Mechanics 2017

The course TME131 Project in Applied Mechanics is a mandatory course within the AppliedMechanics Masters programme at Chalmers. The course was carried out during springsemester 2017. In total 7 projects were carried out, and 4 of these are collected here

Experimental and Numerical Study of Laminar-Turbulent Transition on a Low-Pressure Turbine Outlet Guide Vane

This work presents an experimental and numerical investigation on the laminar-turbulent transition and secondary flow structures in a Turbine Rear Structure (TRS). The study was executed at engine representative Reynolds number and inlet conditions at three different turbine load cases. Experiments were performed in an annular rotating rig with a shrouded low-pressure turbine upstream of a TRS test section. The numerical results were obtained using the SST k–ω turbulence model and the Langtry- Menter γ–θ transition model. The boundary layer transition location at the entire vane suction side is investigated. The location of the onset and the transition length are measured using IR thermography along the entire vane span. The IR-thermography approach was validated using hot-wire boundary layer measurements. Both experiments and CFD show large variations of transition location along the vane span with strong influences from endwalls and turbine outlet conditions. Both correlate well with traditional transition onset correlations near midspan and show that the transition onset Reynolds number is independent of the acceleration parameter. However, CFD tends to predict an early transition onset in the midspan vane region and a late transition in the hub region. Furthermore, in the hub region, CFD is shown to overpredict the transverse flow and related losses.Disclaimer:\ua0The content of this article reflects only the authors’ view. The Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains

Experimental heat transfer study in an intermediate turbine duct

Due to demands from industry on improved efficiency, reduced CO2 and NOx and decreased noise levels, the trend of future aero engines show that turbofan engines are designed with higher by-pass ratio. Two-spool and three-spool turbofan engines are designed with an intermediate turbine duct that connects the high-pressure turbine to the low-pressure turbine in the two-spool engine and two intermediate turbine ducts from HPT to intermediate pressure turbine (IPT) and IPT to LPT in the three-spool engines. The design of agressive intermediate turbine ducts (high radial offset for a short axial length) for these engines enables the possibility to increase the energy efficiency of the aero engine. The flow and heat transfer in a turbine duct is very complex. The flow has large secondary structures and is sensitive to flow separation, which is difficult to predict with numerical methods. Limited information is available in open literature that can be used for validation of numerical methods. This paper presents an experimental study of the heat transfer in an aggressive intermediate turbine duct. The aim of this study is to measure the of a surface temperature distribution and convection heat transfer coefficient with very high resolution and precision on a loaded guide vane which is located inside the intermediate turbine duct. Furthermore, the experimental results are compared to CFD carried out with ANSYS CFX. This experiment was carried out in a state-of-the-art large-scale low-speed turbine facility at Chalmers University of Technology. The duct configuration investigated represents a modern counter rotating turbine design, with a flow turning structural vane. The facility includes a turbine stage which provides realistic inlet conditions into the duct and operates at realistic flow Reynolds number based on the ITD vane chord length. The measurements were performed by using an infrared camera. The results shows that the heat transfer coefficient predicted in the computations close to the shroud is not well predicted. There can also be seen areas where there is flow transition and boundary layer transition