1,721,084 research outputs found
UNSTRUCTURED PERIODIC GRID GENERATION AROUND 2D TURBINE CASCADES
No full textA novel grid generation algorithm for periodic unstructured grid around two-dimensional highly-staggered turbine cascades, including multiply connected blade geometries, is presented. The idea is to generate the mesh in a transformed space in which the periodic boundaries are coincident and internal to the computational domain so that no special treatment along these curves is required. The mesh in the transformed u-v space is computed by means of front-advancing/Delaunay technique and the resulting grid is transformed back into the x-y space of physical variables after introducing a suitable cut, which translates to periodic boundaries in the x-y plane. The cut is not arbitrary and it is automatically managed by the algorithm. The proposed transformation is conformal and therefore no elements are distorted in the process. In this way, the prescribed element size and mesh quality are easily attained and the uniqueness of the periodic nodes is guaranteed by the fact that they are indeed coincident in the space u-v. Numerical simulations of a VKI LS-89 turbine blade are presented to support the present approach
Multi-physics simulation of in-flight ice shedding
Full text linkIn-flight ice accretion may possibly jeopardise the safety of fixed-and rotary-wing aircraft. Icing can possibly occur if supercooled water droplets in clouds impinge on the aircraft surfaces and freeze upon impact. A major issue related to ice accretion is the possibility of ice shedding from the main body and impacting other parts of the aircraft or being ingested by the engines. A multi-physics framework is presented to simulate ice accretion and shedding from wings and engine nacelles due to aerodynamic forces. The aerodynamics is computed using the open-source tool-kit SU2. Cloud droplet trajectories are computed using the arbitrary-precision Lagrangian in-house solver PoliDrop. Then, the in-house ice accretion tool-kit PoliMIce is used to determine the ice layer. A FEM structural analysis is performed on the accreted ice shape by means of the open-source code MoFEM. Internal stresses within the ice geometry due to aerodynamic forces are computed. The possibility of the occurrence of cracks in the ice layer is assessed and its propagation is determined numerically. Two-dimensional ice accretion simulations are performed to check the validity of the present approach and compare fairly well with available results
Ideal and non-ideal planar compressible fluid flows in radial equilibrium
Full text linkTwo-dimensional compressible flows in radial equilibrium are investigated in the ideal dilute-gas regime and the non-ideal single-phase regime close to the liquid-vapour saturation curve and the critical point. Radial equilibrium flows along constant-curvature streamlines are considered. All properties are therefore independent of the tangential streamwise coordinate. A differential relation for the Mach number dependency on the radius is derived for both ideal and non-ideal conditions. For ideal flows, the differential relation is integrated analytically. Assuming a constant specific heat ratio gamma, the Mach number is a monotonically decreasing function of the radius of curvature for ideal flows, with gamma being the only fluid-dependent parameter. In non-ideal conditions, the Mach number profile also depends on the total thermodynamic conditions of the fluid. For high molecular complexity fluids, such as toluene or hexamethyldisiloxane, a non-monotone Mach number profile is admissible in single-phase supersonic conditions. For Bethe-Zel'dovich-Thompson fluids, non-monotone behaviour is observed in subsonic conditions. Numerical simulations of subsonic and supersonic turning flows are carried out using the streamline curvature method and the computational fluid dynamics software SU2, respectively, both confirming the flow evolution from uniform flow conditions to the radial equilibrium profile predicted by the theory
A simulation framework for rotorcraft ice accretion and shedding
Full text linkIn this work a novel three-dimensional simulation framework for modelling the safety critical problem of rotorcraft ice formation and shedding is presented. To enable an entirely three-dimensional framework, state-of-the-art numerical modelling techniques are adopted and the inter-dependency between the techniques is discussed. The numerical techniques introduced in this work include models to simulate the rotor flow-field, water droplet trajectories and impingement locations, phase change modelling during the ice accretion, and mesh deformation to account for the moving ice boundary. A set of benchmark test cases are initially used for preliminary validation of the icing framework. This allows for a comparison of the collection efficiency and ice shapes with high-quality experimental measurements. Icing wind tunnel tests conducted on the Spinning Rotor Blade (SRB-II) model rotor are used for an assessment of the numerical predictions specific to rotorcraft. Quantities used for comparisons include the ice thickness and shedding location. Numerical predictions are in good agreement with the measured data at all temperatures. Additionally, the outcome of influential parameters which directly impact rotor ice shapes are assessed. In particular, the model for the temperature profiles within the ice layer, and the centrifugally induced movement of the liquid film
Non-Ideal Compressible Fluid Dynamics: Preface
No full textNon-ideal compressible fluid dynamics (NICFD) is
the branch of fluid-mechanics concerning the study of
non-reacting flows of fluids in non-ideal thermodynamic
states. It therefore deals with dense vapor flows, vaporliquid flows, supercritical and near-critical fluid flows,
and compressible liquid flows
An adaptive ALE scheme for non-ideal compressible fluid dynamics over dynamic unstructured meshes
Full text linkThis paper investigates the application of mesh adaptation techniques in the non-ideal compressible fluid dynamic (NICFD) regime, a region near the vapor–liquid saturation curve where the flow behavior significantly departs from the ideal gas model, as indicated by a value of the fundamental derivative of gasdynamics less than one. A recent interpolation-free finite-volume adaptive scheme is exploited to modify the grid connectivity in a conservative way, and the governing equations for compressible inviscid flows are solved within the arbitrary Lagrangian–Eulerian framework by including special fictitious fluxes representing volume modifications due to mesh adaptation. The absence of interpolation of the solution to the new grid prevents spurious oscillations that may make the solution of the flow field in the NICFD regime more difficult and less robust. Non-ideal gas effects are taken into account by adopting the polytropic Peng–Robinson thermodynamic model. The numerical results focus on the problem of a piston moving in a tube filled with siloxane (Formula presented.), a simple configuration which can be the core of experimental research activities aiming at investigating the thermodynamic behavior of NICFD flows. Several numerical tests involving different piston movements and initial states in 2D and 3D assess the capability of the proposed adaption technique to correctly capture compression and expansion waves, as well as the generation and propagation of shock waves, in the NICFD and in the non-classical regime
Wall-resolved large eddy simulations of a pitching airfoil in deep dynamic stall
Full text linkThis study investigates the flow evolution around a sinusoidal pitching NACA 0012 airfoil, defined by the National Advisory Committee for Aeronautics, undergoing deep dynamic stall using a wall-resolved large eddy simulation (LES) approach. Numerical results are assessed against experimental data from Lee and Gerontakos (2004) at a Reynolds number Re = 135 000 and reduced frequency k = 0.1. A comprehensive analysis of the computational model span size is presented, highlighting the requirement for a span-to-chord ratio of at least one to correctly capture the dynamic stall vortex physics in the downstroke phase. Furthermore, a comparative assessment with state-of-the-art Reynolds-Averaged Navier-Stokes (RANS), hybrid RANS/LES, and the experimental data is carried out. All the numerical models concur to the same flow behavior and exhibit similar differences with the experiments
An ALE Interpolation-Free Strategy for Unsteady Flow Simulations Using Finite Volume and Residual Distribution Schemes over Adaptive Grids
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