Marcos de Mattos Pimenta

Laminar-Turbulent Transition Modeling Strategies for Thermally Protected Airfoils

The present article discusses some of the transition modeling strategies typically applied by the industry. Transition effects on the heat transfer characteristics and calculation for airfoil anti-ice protection systems build the framework of the developments of interest. Results of the studied models are presented for flat plate data taken from the ERCOFTAC experiments.Copyright

Liquid Jet Flashing into a Low Pressure Environment: A Numerical Solution

A numerical study of flashing jet s of superheated or metastable liquids is presented. The analysis is valid for a superheated liquid that changes phase across an oblique evaporation wave . Next, it is accelerated to supersonic velocities as i t expands to a low pressure environment to, fin ally, undergo a pressure adjusting process through a regular compression shock wave. The two -phase high velocity fluid flow is modeled in a 2 D region axis -symmetric region . The governing equations for this phenomenon are: mass, momentum, energy conservati on , and a real state equation. The system of equations was solved in the conservative form and steady state. A structu red grid wa s used in the numerical domain and the MacCor mack finite differences scheme ha s been employed. Due to the na ture of the metho d which only solves the supersonic expansion process, it was needed to solv e the shock wave, a simple capturing shock capturing scheme was implemented along with a grid refinement process . Nomenclature b A = nozzle exit section area m a = tangent of the slant height of the cone trunk D C = discharge coefficient x C = non -dimensional parameter of artificial viscosity z

The Similarity of Ducted Jets With Low and High Pressure Gradients

The objective of the present work is to study what type of effects the dimensionless jet parameters really consider. To do it, three classical dimensionless jet parameters are redeveloped using an unified methodology. This methodology is based on the integral balances of mass and momentum. The momentum balance terms are classified as inertial or pressure terms and as flux or source terms. This redevelopment enlighten the meaning of the dimensionless jet parameters and allows the definition of a new set of parameters. A scaling methodology is presented to compare the dimensionless jet parameters adequacy in scaling center line jet velocity and jet width at different operational conditions. Two regimes are distinguished: low pressure gradient and high pressure gradient. The scaling for low pressure gradient is based on two criteria: the diffusivity ratio proportionality and the linear expansion rate of the jet. The diffusivity is modelled using the Prandtl’s mixing length model and a dimensional analysis based only on inertial momentum terms. The scaling for high pressure gradient is based on jet velocities and widths scaled simultaneously by pressure and inertial momentum terms. The application of this methodology to jet literature data shows jet similarity for low and high pressure gradients. However, some drawbacks are identified in scaling the jet width at high pressure gradients.Copyright

An Interpretation for Dimensionless Jet Parameters: Three Classics and one New

The objective of the present work is to study what type of effects the dimensionless jet parameters really consider. To do it, three classical dimensionless jet parameters are redeveloped using an unified methodology. This methodology is based on a momentum balance that considers momentum fluxes at the inlet surface, at the outlet surface and a momentum source term. The momentum balance terms are classified as inertial or pressure terms and as flux or source terms. This redevelopment enlighten the meaning of the dimensionless jet parameters and allows the definition of a new improved parameter. A scaling methodology is presented to compare the dimensionless jet parameters adequacy in scaling center line jet velocity and jet radius at different jet operational conditions. The scaling methodology is based on the Prandtl’s mixing length model and on the Q theorem. The application of this methodology to jet literature data shows the superiority of the new dimensionless jet parameter.

Simulating Transition with an Intermittency Transport Equation in a Commercial Solver

As a result of recent developments in the field of thermal anti-ice protection of airfoils, was identified the relevance of accurately modeling the transitional boundary layer in order to predict the external heat transfer coefficient. In thisarticle the capability of a low-Reynolds k-ǫ model in the evaluation of transition for a flat plate is tested. The coupling of an intermittency transport function with the native turbulence model of a commercial solver is proposed as an efficient alternative to improve prediction of some transition features. The model was implemented and tested for two freestream turbulence levels. The results are compared with experiments and with those obtained with the original low-Reynolds k-ǫ model without the modifications. Both the skin friction coefficient a boundary layer shape factor evolution calculated with the coupled intermittency transport function showed good agreement with experiments.