The development of high-performance turbine airfoils has been investigated under the condition of a supersonic exit Mach number. In order to obtain a new aerodynamic design concept for a high-loaded turbine rotor blade, we employed an evolutionary algorithm for numerical optimization. The target of the optimization method, which is called evolutionary strategy (ES), was the minimization of the total pressure loss and the deviation angle. The optimization process includes the representation of the airfoil geometry, the generation of the grid for a blade-to-blade computational fluid dynamics analysis, and a two-dimensional Navier-Stokes solver with a low-Re k-ε turbulence model in order to evaluate the performance. Some interesting aspects, for example, a double shock system, an early transition, and a redistribution of aerodynamic loading on blade surface, observed in the optimized airfoil, are discussed. The increased performance of the optimized blade has been confirmed by detailed experimental investigation, using conventional probes, hotfilms, and L2F system.
The flow in a transonic turbine rotor cascade is investigated by both experimental and numerical methods. Measurements include pressure profiles on the blade, total pressure profiles in the blade vane, boundary-layer and wake profiles. Computations are performed by two different solvers with different turbulence models and three different transition models. Results indicate that the introduction of transition models is necessary to have a realistic description of the flow field. Transition is shown to affect also the blade pressure distribution and shock strength mostly on the pressure side boundary layer. Experiments indicate the presence of trailing edge vortex shedding which is not captured by the steady computations. The transition models seem adequate for predicting the shock-boundary layer interaction which induces a small flow separation on the suction side.
The development of high performance turbine airfoils has been investigated under the condition of a supersonic exit Mach number. In order to obtain a new aerodynamic design concept for a high loaded turbine rotor blade, we employed an evolutionary algorithm for numerical optimization. The target of the optimization method, which is called evolution strategy (ES), was the minimization of the total pressure loss and the deviation angle. The optimization process includes the representation of the airfoil geometry, the generation of the grid for a blade-to-blade CFD analysis, and a 2D Navier-Stokes solver with a low-Re k-ε turbulence model in order to evaluate the performance. Some interesting aspects, for example, a double shock system, an early transition and a re-distribution of aerodynamic loading on blade surface, observed in the optimized airfoil, are discussed. The increased performance of the optimized blade has been confirmed by detailed experimental investigation, using conventional probes, hot-films and L2F system.
This paper describes the aerodynamic optimization of a typical exhaust diffuser for a heavy duty gas turbine. The objective is to maximize diffuser performance and, in this way, pressure recovery by optimizing the geometry for two given inlet conditions. To validate and adjust the numerical set-up, experimental data from measurements on the test model is used. The numerical results obtained by using TRACE compares with the experimental results. An optimization process is applied using the framework AutoOpti developed by DLR, which combines evolutionary strategies with surrogate models in order to select optimal geometric parameters. Finally, the differences between the baseline and several optimized designs are discussed and the impact of different parameters on diffuser performance is demonstrated.
Exhaust diffusers of heavy duty gas turbines significantly improve the performance of gas turbines. These diffusers typically differ from the simple and well investigated annular or conical diffusers because of the incorporated struts. The investigated model of such a typical exhaust diffuser consists of an annular duct with two rows of integrated struts and a Carnot diffuser downstream of the annular part. In this paper the influence of inlet blockage on the performance of gas turbine diffusers is numerically investigated. 3D-RANS calculations are performed applying the k-ω-SST-model. The numerical inlet conditions for the baseline are given by detailed experimental data acquired in a test rig. The results show that the impact of the inlet blockage on the diffuser flow can be split into two aspects, which both influence diffuser pressure recovery. The first aspect is the well-known reduction of effective area of the core flow leading to reduced pressure recovery feasibility. Secondly, it is observed that the inlet blockage has a significant influence on the structure of secondary flow in the vicinity of the diffuser struts affecting the diffuser pressure recovery. Using a simple correlation of the size of the secondary flow and the core flow the influence on pressure recovery is estimated. In sum, the aerodynamic performance of the annular diffuser and the first row of strut is of high importance and mainly depends on the inlet boundary conditions. Accordingly, these geometries need to be designed to their inlet conditions.
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