Design A Micro Hydro Turbine
The shapes of the runners are rather complicated and therefore the understanding of he complex geometry and especially of the spatial structures of the flow are very difficult to analyze by two-dimensional display tools. Many deferent views and cuts have to be prepared and analyzed, which Is quite uneconomical and time consuming. In a virtual reality environment, however, the complex geometry and especially the flow behavior can be controlled much faster and in more detail. This is particularly the case for students, who are not completely familiar with turbine shapes.
Consequently a design tool based on IVR-techniques is developed at IIS and RUSS. The yester Is used for educational purposes as well as for Industrial applications. The primary design is obtained on the basis of Lure’s equation for turbocharger. The design parameters such as head, discharge, speed, number of blades can be changed by sliders. Other parameters, e. G. Blade angle can be manipulated by Interaction In IVR using AD Interaction devices. Since Lure’s equation Is relatively simple the geometrical shape can be calculated online. Therefore many sets of parameters can be investigated and optimized in a short time.
After the primary design the blade shape is fixed and can then be analyzed by numerical flow simulation. The flow calculation, based on the Never-Stokes equations, can be carried out on a supercomputer in order to achieve a short response time. The calculated flow behavior is studied in the IVR-environment. Again, it is much easier to understand the complex relations between the flow and the geometry In IVR than using two-dimensional display facilities, This Is principally of great Importance for people not entirely accustomed with turbine runner flows.
Consequently the IVR-environment is particularly important for educational purposes. Visualization Software COVES Is a software environment developed by the Computer Center (RUSS) which tries to Integrate visualization and simulation tasks across heterogeneous hardware platforms in a seamless manner. The user interface is based on the visual programming paradigm. Distributed applications can be built by combining modules ‘OFF form more or less complex module networks. At the end of such networks usually the rendering step does the final visualization.
A special feature of COVES is that it allows several users to work in a collaborative way providing online consulting to end users at remote sites or tell-teaching. For the visualization COVES supports desktop as well as IVR oriented rendered modules. Hardware equipment For the IVR based visualization two different environments are used, one at IIS and one at RUSS. In both environments the visualization runs on local SSI workstations, the flow simulation program runs on the super-computers of HALL (HГ¶chstleistungsrechenzentrum Stuttgart) either on a NECK SEX-4 vector computer or on a CRAY TEE computer in parallel.
The workstations and the super-computers are connected either by a high speed network (HIPPIE, ATM) or by FIDE. The environment is schematically shown in fig. 1. CRAY TEE 512 RUSS Help environment SSI onyx EDDIE IIS NECK SEX-4 SSI Crimson HALL Fig. 1: Working environment a single wall back projection system driven by a SSI Realigning system, see fig. 2. A four side back projection system called the CUBE is installed at RUSS. The CUBE is connected too Silicon Graphics Onyx double rack system with 14 ARROYO CUPS and BIB of main memory.
The Onyx has three Inferentially pipes each equipped with two raster managers. Several magnetic tracking systems such as Populous Fastback with Stylus pen and the Ascension Motions with AD mouse are supported for the interaction of the user tit the virtual environment. Fig. 2: IVR equipment at IIS Design System It is a parametric design system based on Lure’s equation for turbocharger. Using this equation the flow angles upstream as well as downstream of the runner can be calculated that are needed to produce the runner torque necessary for the required turbine power output.
These flow angles are transformed to blade angles taking into account knowledge based assumptions for incidence and deviation angles. In between, from leading to trailing edge of the blade, mean lines are created and profile coordinates are added taken from catalogue. Then, curvature and thickness distributions are optimized using CUFF in order to define the final blade shape. Simulation software The flow simulation is carried out using FENNEL’S, a finite element flow simulation program, developed at IIS. It is based on the Reynolds averaged Navies-Stokes equations -2- with various models of turbulence.
Usually the k-E model is used. FENNEL’S runs on various platforms ranging from PC to vector-supercomputers and massively parallel machines. The personalization is obtained by a domain decomposition algorithm with overlapping meshes. For the online simulation FENNEL’S has been integrated into COVES as a module. Application The application shown in this paper is an axial propeller turbine. The geometry of the adjustable guide vanes and of the fixed runner blades is shown in fig. 3. The turbine is main data: ; Head: 7. 9 m ; Discharge: 5. Mm/s ; Speed: 250 RPM ; No of runner blades: 6 By using the design system the influence of the different parameters can be easily demonstrated. So the students as well as the industrial customers can get impression of the blade shape very fast. As an example in fig. 4 the runner blades are shown Fig. 3: Geometry of an axial propeller turbine or the data described above as well as for a reduced discharge rate of 4 Mm/s keeping all other parameters constant. The influence of the discharge can be seen clearly. For the high flow rate the runner blades are steeper.
By reducing the flow rate the inlet and outlet angles of the blades have to be more flat and consequently the blade channel is becomes narrower. A) high discharge rate b) lower discharge rate Fig. 4: Runner blades design for two different discharge rates As already mentioned after the preliminary investigation of the blade shapes the flow in the runner is calculated numerically. For this calculation a computational grid is needed. Usually a periodical flow condition is assumed. Consequently only one channel of the runner has to -3- be considered.
The grid is obtained by a specialized grid generator. A typical grid around a runner blade is shown in fig. 5. A typical grid consists of approximately 100000-200000 nodes. The flow is calculated in a frame of reference rotating with the runner. In this frame the state. During the simulation the results are sent from time to time to COVES and displayed in the IVR environment. The current iteration step as well as the final results can than be analyzed interactively using IVR techniques. For example particle traces or streamlines can be started, cutting planes can be located according to the Fig. : Computational grid around the runner blade users requirements etc. This allows a fast understanding of the complete three-dimensional flow structure. In fig. 6 the distribution of streamlines at the hub for the shown geometry is presented. It can be seen, that the flow angle corresponds quite well to the blade angle. This is usually the most critical part of the blade. Conclusion A tool for the design of hydro turbine runner is under development for educational and industrial purposes, respectively. The tool is based on Virtual Reality technique.
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