The von Karman Institute for Fluid Dynamics is a non-profit educational and scientific organization which specializes in three specific fields: aeronautics and aerospace, environment and applied fluid dynamics, turbomachinery and propulsion. Founded in 1956, it is located in Sint-Genesius-Rode, Belgium. Wikipedia.
Panesi M.,University of Illinois at Urbana - Champaign |
Lani A.,Von Karman Institute for Fluid Dynamics
Physics of Fluids | Year: 2013
We present a reduced kinetic mechanism for the modeling of the behavior of the electronic states of the atomic species in air mixtures. The model is built by lumping the electronically excited states of the atomic species and by performing Maxwell-Boltzmann averages of the rate constants describing the elementary kinetic processes of the individual states within each group. The necessary reaction rate coefficients are taken from the model compiled by Bultel et al. ["Collisional-radiative model in air for earth re-entry problems," Phys. Plasmas13, 043502 (2006)10.1063/1.2194827]. The reduced number of pseudo-states considered leads to a significant reduction of the computational cost, thus enabling the application of the state of the art collisional radiative models to bi-dimensional and three-dimensional problems. The internal states of the molecular species are assumed to be in equilibrium. The rotational energy mode is assumed to quickly equilibrate with the translational energy mode at the kinetic temperature of the heavy species as opposed to the electronic and the vibrational modes, assumed to be in Maxwell-Boltzmann equilibrium at a common temperature TV. In a first step we validate the model by using simple zero- and one-dimensional test cases for which the full kinetic mechanism can be run efficiently. Finally, the reduced kinetic model is used to analyze the strong non-equilibrium flow surrounding the FIRE II flight experiment during the early part of its re-entry trajectory. It is found that the reduced kinetic mechanism is capable of reproducing the ionizational non-equilibrium phenomena, responsible for the drastic reduction of the radiative heat loads on the space capsules during the re-entry phase. © 2013 AIP Publishing LLC.
Buchlin J.M.,Von Karman Institute for Fluid Dynamics
Journal of Applied Fluid Mechanics | Year: 2011
The paper deals with heat transfer by convection between impinging gas jets and solid surfaces. It considers both single and multiple jet systems. It emphasizes the flow and geometrical parameters as well as the environment conditions at which the jet emerges. In particular, it points out the effect of the jet tilting, thermal entrainment and jet confinement. ASN and ARN schemes are illustrated through industrial and aeronautical applications. Design correlations are proposed. Experimental data obtained from infrared thermography are compared to CFD simulations.
Munafo` A.,Von Karman Institute for Fluid Dynamics |
Magin T.E.,Von Karman Institute for Fluid Dynamics
Physics of Fluids | Year: 2014
The stagnation-line flow over re-entry bodies is analyzed by means of a quantum based collisional model which accounts for dissociation and energy transfer in N2-N interactions. The physical model is based on a kinetic database developed at NASA Ames Research Center. The reduction of the kinetic mechanism is achieved by lumping the rovibrational energy levels of the N2 molecule in energy bins. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The governing equations are discretized in space by means of the Finite Volume method. A fully implicit time-integration is used to obtain steady-state solutions. The results show that the population of the energy bins strongly deviate from a Boltzmann distribution close to the shock wave and across the boundary layer. The sensitivity analysis to the number of energy bins reveals that accurate estimation of flow quantities (such as chemical composition and wall heat flux) can be obtained by using only 10 energy bins. A comparison with the predictions obtained by means of conventional multi-temperature models indicates that the former can lead to an overestimation of the wall heat flux, due to an inaccurate modeling of recombination in the boundary layer. © 2014 AIP Publishing LLC.
Sakraker I.,Von Karman Institute for Fluid Dynamics |
Asma C.O.,Von Karman Institute for Fluid Dynamics
Journal of the European Ceramic Society | Year: 2013
The passive/active oxidation behavior of a CVD-SiC coated C/C-SiC thermal protection material of the hypersonic SpaceLiner vehicle is investigated experimentally. For the safety of spacecraft and its passengers, it is important to know whether the thermal protection system will experience passive/active oxidation during the vehicle's entry into Earth's atmosphere. Active oxidation can promote material loss whereas passive oxidation forms a protective film. The high enthalpy flight conditions of SpaceLiner vehicle are duplicated in VKI Plasmatron, where the samples are exposed to high enthalpy plasma and the surface temperatures increase up to 2800 K at various total pressure (2-20 kPa) conditions. Surface temperature profiles, visual characteristics, mass changes, emissivity, spectrometer and SEM/EDX data are examined to identify the oxidation transition border of the tested material. A temperature jump is observed in all active oxidation regimes. The experimental results are found to be in good agreement with correlations from the literature. © 2012 Elsevier Ltd.
Fernandez-Villace V.,Von Karman Institute for Fluid Dynamics |
Paniagua G.,Von Karman Institute for Fluid Dynamics
Energies | Year: 2013
Efficient high speed propulsion requires exploiting the cooling capability of the cryogenic fuel in the propulsion cycle. This paper presents the numerical model of a combined cycle engine while in air turbo-rocket configuration. Specific models of the various heat exchanger modules and the turbomachinery elements were developed to represent the physical behavior at off-design operation. The dynamic nature of the model allows the introduction of the engine control logic that limits the operation of certain subcomponents and extends the overall engine operational envelope. The specific impulse and uninstalled thrust are detailed while flying a determined trajectory between Mach 2.5 and 5 for varying throttling levels throughout the operational envelope. © 2013 by the authors.
Lani A.,Von Karman Institute for Fluid Dynamics |
Panesi M.,University of Texas at Austin |
Deconinck H.,Von Karman Institute for Fluid Dynamics
Communications in Computational Physics | Year: 2013
Amulti-dimensionally upwind conservative ResidualDistribution algorithm for simulating viscous axisymmetric hypersonic flows in thermo-chemical nonequilibrium on unstructured grids is presented and validated in the case of the complex flowfield over a double cone configuration. The resulting numerical discretization combines a state-of-the-art nonlinear quasi-monotone second order blended scheme for distributing the convective residual and a standard Galerkin formulation for the diffusive residual. The physical source terms are upwinded together with the convective fluxes. Numerical results show an excellent agreement with experimental measurements and available literature. © 2013 Global-Science Press.
Roger M.,École Centrale Lyon |
Schram C.,Von Karman Institute for Fluid Dynamics |
Moreau S.,Université de Sherbrooke
Journal of Sound and Vibration | Year: 2014
A linear analytical model is developed for the chopping of a cylindrical vortex by a flat-plate airfoil, with or without a span-end effect. The major interest is the contribution of the tip-vortex produced by an upstream rotating blade in the rotor-rotor interaction noise mechanism of counter-rotating open rotors. Therefore the interaction is primarily addressed in an annular strip of limited spanwise extent bounding the impinged blade segment, and the unwrapped strip is described in Cartesian coordinates. The study also addresses the interaction of a propeller wake with a downstream wing or empennage. Cylindrical vortices are considered, for which the velocity field is expanded in two-dimensional gusts in the reference frame of the airfoil. For each gust the response of the airfoil is derived, first ignoring the effect of the span end, assimilating the airfoil to a rigid flat plate, with or without sweep. The corresponding unsteady lift acts as a distribution of acoustic dipoles, and the radiated sound is obtained from a radiation integral over the actual extent of the airfoil. In the case of tip-vortex interaction noise in CRORs the acoustic signature is determined for vortex trajectories passing beyond, exactly at and below the tip radius of the impinged blade segment, in a reference frame attached to the segment. In a second step the same problem is readdressed accounting for the effect of span end on the aerodynamic response of a blade tip. This is achieved through a composite two-directional Schwarzschild's technique. The modifications of the distributed unsteady lift and of the radiated sound are discussed. The chained source and radiation models provide physical insight into the mechanism of vortex chopping by a blade tip in free field. They allow assessing the acoustic benefit of clipping the rear rotor in a counter-rotating open-rotor architecture. © 2013 Elsevier Ltd.
Munoz-Esparza D.,Von Karman Institute for Fluid Dynamics |
Sanmiguel-Rojas E.,University of Jaén
Computers and Fluids | Year: 2011
Helical wire coils fitted inside a round pipe is a simple and well-known heat transfer enhancement technique in order to improve the overall performance of heat exchangers. Three-dimensional numerical simulations of the incompressible laminar flow that develops into smooth round pipes of diameter, d, with wire coil inserts of helical pitch, p, and diameter, e, have been accomplished with the finite volume method. In particular, we describe the behaviour of the Fanning friction factor, f, as a function of the Reynolds number, Re=ρUd/μ, where, U=4Q/πd2, is the mean velocity based in the flow rate, Q, and ρ and μ the density and dynamic viscosity of the fluid, respectively. For a wire coil of 40 pitches in length with dimensionless pitch p/d=2.5 and dimensionless wire diameter e/d=0.074, both pitch-periodic and full domain numerical results have been validated with experiments. We have found an excellent agreement with both numerical models and experimental results for Re<500, showing the friction factor a quasi-linear dependence on Re when is plotted in log-log axes. For 500
Parente A.,Von Karman Institute for Fluid Dynamics |
Parente A.,University of Pisa |
Galletti C.,University of Pisa |
Tognotti L.,University of Pisa
Proceedings of the Combustion Institute | Year: 2011
The direct implementation into CFD codes of large kinetic mechanisms for the prediction of pollutant emissions is still unfeasible, due to computer time limitations which become particularly relevant when considering the typical scale of the industrial applications. Therefore, simplified modeling approaches are generally adopted, as they allow reducing the computational effort associated with the numerical simulations. With regard to NO formation, simple one-step mechanisms are used to describe each of the relevant routes contributing to the overall generation of NO, i.e., thermal, prompt. The main drawback associated to a simplified NO formation approach lies, however, in the extreme sensitivity of the lumped rates on the thermo chemical state which define the combustion system of interest. Then, a proper description of turbulence/chemistry interactions must be employed in the CFD model, to provide a realistic background for the estimation of NO emissions. This becomes particularly important in MILD combustion regime, which generally requires an accurate description of the gas-phase oxidation, due to the kinetic control on the overall combustion process. The present paper discusses key aspects and requisite for predicting NO formation in MILD combustion regime. The approach is based on the direct coupling of simplified NO mechanisms to the CFD calculation and is applied to different MILD conditions. Simulations are carried out for a set of experimental runs performed on a self-recuperative MILD burner, varying the hydrogen content in the fuel stream from 0% up to 50% by wt. © 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Buchlin J.M.,Von Karman Institute for Fluid Dynamics
Journal of Applied Fluid Mechanics | Year: 2010
The paper deals with the application of the infrared thermography to the determination of the convective heat transfer coefficient in complex flow configurations. The fundamental principles upon which the IRTh relies are reviewed. The different methods developed to evaluate the heat exchange are described and illustrated through applications to the aerospace and aeronautical field as well as to the industrial processes.