Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session L28: Industrial Applications I: Turbines and Engines |
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Chair: John Cimbala, The Pennsylvania State University Room: 32A |
Monday, November 19, 2012 3:35PM - 3:48PM |
L28.00001: POD- Mapping and analysis of hydroturbine exit flow dynamics Morten Kjeldsen, Pal Henrik Finstad Pairwise radial dynamic measurements of the swirling draft tube flow have been made at the 25 MW Svorka power plant in Surnadal operating at 48{\%} load at 6 radial and 7 angular positions. The data is analyzed with traditional methods as well as with POD. The measurements were made in the turbine draft tube/exit flow in an axial measurement plane about 1200mm downstream the turbine runner. The draft tube diameter in the measurement plane is about 1300mm. The flow rate during measurements was close to 5.8m3/s. Two probes were used; both of length Le=700 mm and made of stainless steel with an outer diameter of Do=20 mm and inner diameter Di=4mm. At the end of each probe a full bridge cylindrical KULITE xcl152, 0-3.5, was mounted. 90 seconds samples at 10 kS/s were taken. The POD analysis largely follows that of Tutkun et al (see e.g. AIAA J., 45,5,2008). The analysis shows that 26{\%} of the pressure pulsation energy can be addressed to azimuthal mode 1. [Preview Abstract] |
Monday, November 19, 2012 3:48PM - 4:01PM |
L28.00002: Caution: Precision Error in Blade Alignment Results in Faulty Unsteady CFD Simulation Bryan Lewis, John Cimbala, Alex Wouden Turbomachinery components experience unsteady loads at several frequencies. The rotor frequency corresponds to the time for one rotor blade to rotate between two stator vanes, and is normally dominant for rotor torque oscillations. The guide vane frequency corresponds to the time for two rotor blades to pass by one guide vane. The machine frequency corresponds to the machine RPM. Oscillations at the machine frequency are always present due to minor blade misalignments and imperfections resulting from manufacturing defects. However, machine frequency oscillations should not be present in CFD simulations if the mesh is free of both blade misalignment and surface imperfections. The flow through a Francis hydroturbine was modeled with unsteady Reynolds-Averaged Navier-Stokes (URANS) CFD simulations and a dynamic rotating grid. Spectral analysis of the unsteady torque on the rotor blades revealed a large component at the machine frequency. Close examination showed that one blade was displaced by $0.0001^{\circ}$ due to round-off errors during mesh generation. A second mesh without blade misalignment was then created. Subsequently, large machine frequency oscillations were not observed for this mesh. These results highlight the effect of minor geometry imperfections on CFD solutions. [Preview Abstract] |
Monday, November 19, 2012 4:01PM - 4:14PM |
L28.00003: Effect of Marine Hydrokinetic array configuration on power extraction Michael Volpe, Maria Laura Beninati, Michael Krane, Arnie Fontaine Experiments are presented to explore how the spatial arrangement of a Marine Hydrokinetic (MHK) turbine array affects the power extracted from an individual turbine. The experiments were performed in the small-scale testing platform in a hydraulic flume facility (9.8 m long, 1.2 m wide and 0.4 m deep) at Bucknell University. The study focuses on a V-shaped sub-array, with the vertex element in the downstream location. The vertex element is a two-bladed horizontal axis turbine, is loaded using a metal-brush motor, and the two upstream elements are circular perforated disks designed to mimic the time-averaged flow disturbance imparted to the flow by a similar turbine. Experiments were performed for a range of stream-wise separation between the perforated plate elements and the turbine element. For each separation distance, drag on the turbine, power extracted by the turbine, as well as the velocity field upstream and downstream of the turbine, were all measured. From these measurements, the flow incident on the turbine and the rate of work done by the flow on the turbine are obtained. Results show that placing a turbine in the accelerated flow region between the wakes of upstream array elements can result in increased energy extraction. [Preview Abstract] |
Monday, November 19, 2012 4:14PM - 4:27PM |
L28.00004: Numerical modeling of the effects of a free surface on the operating characteristics of Marine Hydrokinetic Turbines Samantha Adamski, Alberto Aliseda Marine Hydrokinetic (MHK) turbines are a growing area of research in the renewable energy field because tidal currents are a highly predictable clean energy source. The presence of a free surface may influence the flow around the turbine and in the wake, critically affecting turbine performance and environmental effects through modification of wake physical variables. The characteristic Froude number that control these processes is still a matter of controversy, with the channel depth and turbine's depth, blade tip depth and diameter as potential candidates for a length scale used in literature. We use the Volume of Fluid model to track the free surface dynamics in a RANS simulation with a BEMT model of the turbine to understand the physics of the wake-free surface interactions. Pressure and flow rate boundary conditions for channel's inlet, outlet and air side have been tested in an effort to determine the optimum set of simulation conditions for MHK turbines in rivers or estuaries. Stability and accuracy in terms of power extraction and kinetic and potential energy budgets are considered. The goal of this research is to determine, quantitatively in non dimensional parameter space, the limit between negligible and significant free surface effects on MHK turbine analysis. [Preview Abstract] |
Monday, November 19, 2012 4:27PM - 4:40PM |
L28.00005: Experimental study of the lift and drag characteristics of a cascade of flat plates in a configuration of interest for tidal energy converters Faical Fedoul, Luis Parras, Carlos del Pino, Ramon Fernandez-Feria Wind tunnel experiments are conducted for the flow around both a single flat plate and a cascade of three parallel flat plates at different angles of incidence to compare their lift and drag coefficients in a range of Reynolds number about $10^5$, and for two values of the aspect ratio of the flat plates. The selected cascade configuration is of interest for a particular type of tidal energy converter. The lift and drag characteristics of the central plate in the cascade are compared to those of the isolated plate, finding that there exist an angle of incidence, which depends on the Reynolds number and the aspect ratio, above which the effective lift of the plate in the cascade becomes larger than that of an isolated plate. These experimental results, which are also analyzed in the light of theoretical predictions, are used as a guide for the design of the optimum configuration of the cascade which extracts the maximum power from a tidal current for a given value of the Reynolds number. [Preview Abstract] |
Monday, November 19, 2012 4:40PM - 4:53PM |
L28.00006: RANS simulations of a flow over a rotating disk: grid sensitivity analysis Svetlana V. Poroseva, Michael A. Snider In industry, a need in accurate and reliable flow simulations often comes with the requirements for reduced computational time and cost. To find an optimal balance between these requirements, a sensitivity analysis of simulation results with respect to various simulations parameters should be conducted at the early stage of computations. When experimental data is not available for validating simulations in a given flow geometry, such study can be conducted for a relevant benchmark problem instead. In the current study, a sensitivity analysis was conducted for flow simulations over a rotating disk. This case can serve as a benchmark problem for flow simulations around a wind turbine, for example. Indeed, as a number of blades on a wind turbine approaches infinity, the turbine's geometry transforms to a solid disk. The convergence of simulation results with respect to the size of computational domain, boundary proximity, grid stretching, and initial grid wall spacing was analyzed for five standard turbulence models available in Star-CCM+ software. Objectives were i) to find the coarsest grid that closely reproduces results obtained with a given turbulence model on more fine grids and ii) to find a model that is more robust to changes in the gird parameters. [Preview Abstract] |
Monday, November 19, 2012 4:53PM - 5:06PM |
L28.00007: Evaluating Fuel-Air Mixing in a Direct-Injection Hydrogen-Fueled Internal Combustion Engine Alireza Ebadi, Christopher White Proper orthogonal decomposition (POD) is used to decompose in-cylinder particle image velocimetry (PIV) vector fields acquired in a direct injection hydrogen-fueled internal combustion engine (DI-H2ICE) into mean, coherent, and incoherent vector fields, where the coherent vector fields are presumed to capture the cycle-variability of the flow. The POD vector fields are then used to investigate the effects of fuel injection timing on in-cylinder turbulence and fuel-air mixing. [Preview Abstract] |
Monday, November 19, 2012 5:06PM - 5:19PM |
L28.00008: Swirling flow in model of large two-stroke diesel engine K.E. Meyer, K.M. Ingvorsen, S. Mayer, J.H. Walther In large two-stroke uniflow scavenged marine diesel engines fresh air is blown in through angled ports in the bottom of the cylinder liner forcing the burned gas out through an exhaust valve in the cylinder head. The scavenging flow is a transient (opening/closing ports) confined port-generated turbulent swirling flow, with complex phenomena such as central recirculation zones, vortex breakdown and vortex precession. A scale model of a simplified cylinder is created with a transparent cylinder five diameters long. The flow in the experiment has a Reynolds number of 50,000 based on the cylinder diameter and bulk velocity. Stereoscopic Particle Image Velocimetry (PIV) is used to investigate the flow for cases with both static and moving piston. Port angles of 0, 10, 20 and 30 degrees are considered. Although the flow has a relatively low swirl number of around 0.4, a central recirculation zone is observed indicating a vortex breakdown. The steady flow is analyzed with proper orthogonal decomposition revealing systematic variations in the shape and location of the vortex core. Transient measurements using phase-locked PIV are carried out with moving piston. The transient measurements reveal a sudden rapid change in flow topology as a central recirculation zone is formed. [Preview Abstract] |
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