Numerical Simulation of Dam-Break Problem Using an Adaptive Meshing Approach

Abstract The numerical simulation of free-surface flows is a vast topic, with applications to various fields of engineering such as aerospace, automotive, nuclear, etc. The Volume of Fluid (VOF) method represents a suitable technique to simulate free surface flows, tracking the air-liquid interface within the calculation domain. However this method requires a very fine mesh to successfully reconstruct the liquid surface, leading to very high computational costs. In this paper, VOF simulations of three-dimensional dam-break problem have been carried out using an adaptive meshing approach. Unsteady calculations have been performed exploiting the adaptive mesh feature implemented in ANSYS Fluent. In particular, a grid adaptation strategy has been defined as a way of significantly reducing the numerical effort. The main idea is to keep high resolution only locally at the air-liquid interface, minimizing numerical diffusion, and to maintain a coarse mesh size elsewhere. The dam-break problem was analyzed because it has been widely studied experimentally and numerically, representing a benchmark problem for verifying numerical models involving free-surface flows. The accuracy of the method has been assessed comparing simulation results with experimental data

Modular approach to analysis of chemically recuperated gas turbine cycles

Current research programmes such as the CAGT programme investigate the opportunity for advanced power generation cycles based on state-of-the-art aeroderivative gas turbine technology. Such cycles would be primarily aimed at intermediate duty applications. Compared to industrial gas turbines, aeroderivatives offer high simple cycle efficiency, and the capability to start quickly and frequently without a significant maintenance cost penalty. A key element for high system performance is the development of improved heat recovery systems, leading to advanced cycles such as the humid air turbine (HAT) cycle, the chemically recuperated gas turbine (CRGT) cycle and the Kalina combined cycle. When used in combination with advanced technologies and components, screening studies conducted by research programmes such as the CAGT programme predict that such advanced cycles could theoretically lead to net cycle efficiencies exceeding 60%. In this paper, the authors present the application of the modular approach to cycle simulation and performance predictions of CRGT cycles. The paper first presents the modular simulation code concept and the main characteristics of CRGT cycles. The paper next discusses the development of the methane–steam reformer unit model used for the simulations. The modular code is then used to compute performance characteristics of a simple CRGT cycle and a reheat CRGT cycle, both based on the General Electric LM6000 aeroderivative gas turbine

Flat plate and turbine vane film-cooling performance with laid-back fan-shaped holes

Shaped holes are considered as an effective solution to enhance gas turbine film-cooling performance, as they allow to increase the coolant mass-flux, while limiting the detrimental lift-off phenomena. A great amount of work has been carried out in past years on basic flat plate configurations while a reduced number of experimental works deals with a quantitative assessment of the influence of curvature and vane pressure gradient. In the present work PSP (Pressure Sensitive Paint) technique is used to detail the adiabatic effectiveness generated by axial shaped holes with high value of Area Ratio close to 7, in three different configurations with the same 1:1 scale: first of all, a flat plate configuration is examined; after that, the film-cooled pressure and suction sides of a turbine vane model are investigated. Tests were performed varying the blowing ratio and imposing a density ratio of 2.5 . The experimental results are finally compared to the predictions of two different correlations, developed for flat plate configurations

Effect of Rotation and Hole Arrangement in Cold Bridge-Type Impingement Cooling Systems

Experimental activity has been performed to study different impingement cooling schemes in static and rotating conditions. Geometry replicates a leading-edge cold bridge system, including a radial supply channel and five rows of film-cooling and showerhead holes. Two impingement geometries have been studied, with different numbers of holes and diameters but with equal overall passage area. Reynolds numbers up to 13,800 and rotation numbers up to 0.002 have been investigated (based on an equivalent slot width). Tests have been performed using a novel implementation of transient heat transfer technique, which allows correct replication of the sign of buoyancy forces by flowing ambient temperature air into a preheated test article. Results show that complex interactions occur between the different features of the system, with a particularly strong effect of jet supply condition. Rotation further interacts with these phenomena, generally leading to a slight decrease in heat transfer

Numerical Identification of a Premixed Flame Transfer Function and Stability Analysis of a Lean Burn Combustor

AbstractCombustion instabilities represent a long known problem in combustion technology. The environment-friendly lean premixed gas turbines exhibit an increased risk of occurrence of thermo-acoustically induced combustion oscillations. In the present work the stability of a lean premixed swirl-stabilized combustor, experimentally studied at Technische Universität of Munich, has been investigated. The complex interaction between the system acoustics and the turbulent swirling flame is studied using unsteady CFD simulations with Flamelet-Generated Manifolds combustion model. Results were validated against experimental data. Perturbations are introduced in the system imposing a broadband excitation as inlet boundary condition. The flame response to the perturbation is then computed and described exploiting system identification techniques. The identified Flame Transfer Function (FTF) shows quantitative agreement with experiment for amplitude and phase, especially for the low frequency range. At higher frequencies the phase prediction slightly deteriorates while the gain is still well described. The obtained results are implemented into a finite element model of the combustor in order to analyze the stability of the system. Results are compared with available experimental data showing a satisfactory agreement. The advantage introduced by a more sophisticated model for FTF is further evidenced comparing the results with those obtained with analytical formulation found in literature

RANS MODELING OF FLOW IN ROTATING CAVITY SYSTEM

The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of gas turbine engine. The selection of a suitable turbulence model for the study of such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of the most used eddy viscosity RANS models available within the commercial CFD solvers Fluent and CFX together with an innovative Reynolds Stress Model closure. The predictions are compared to experimental data and previous numerical calculations available in the open literature for three test cases. Test case 1 corresponds to a rotating cavity with a radial outflow, considered experimentally by Owen and Pincombe. In that case, the main difficulty arises from the choice of the boundary conditions at the outlet. Several types of boundary conditions have been then considered. All models fail to predict the radial velocity distribution. Nevertheless, the RSM offers the best agreement against the experimental data in terms of the averaged tangential velocity in the core. Test case 2 corresponds to a Taylor-Couette system with an axial Poiseuille flow studied experimentally by Escudier and Gouldson. Even if the two-equation models provide reliable data for the mean velocity field, they strongly underestimate the turbulence intensities everywhere. The agreement between the RSM and the measurements is rather satisfactory for the mean and turbulent fields, though this second-order closure does not predict the asymmetry of the normal stresses. The main discrepancies appear indeed very close to the stator. Test case 3 is a rotor-stator system with throughflow, corresponding to the test rig of Poncet et al. All the models catch the main features of rotor-stator flows, such as the value of the entrainment coefficient or the location of the transition from the Stewartson to the Batchelor flow structures. The RSM improves especially the predictions of the shear stress