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Arad E.,Rafael Laboratories | Arad E.,CFD Group | Ramasamy M.,NASA | Wilson J.S.,U.S. Army
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

Numerical and experimental analysis of synthetic jet actuator is reported. The study focuses on the actuator itself and on the vorticity field and structures that are generated by the actuator. Phase-locked, 2-D microscopic-PIV technique (MPIV) was used in experiment, and large eddies simulation (LES) was used for numerical analysis. The two methods were first validated for a circular steady jet, continuing with synthetic jet, emanated from a practical device design to quiescent air. The development of vortical structures and their interactions was carefully studied. The insight obtained is an important building block for better understanding of the interaction of synthetic jets and boundary layers. © 2012 by E. Arad, M. Ramasamy and J. S. Wilson. Source

Bruce P.J.K.,Imperial College London | Babinsky H.,Imperial College London | Tartinville B.,CFD Group | Hirsch C.,Free University of Brussels
AIAA Journal | Year: 2011

An experimental and computational study of aM∞ 1:4 transonic shock wave in a parallel-walled duct subject to downstream pressure perturbations in the frequency range of 16-90 Hz has been conducted. The dynamics of unsteady shock motion and aspects of the unsteady transonic shock and turbulent tunnel-floor boundary-layer interaction have been investigated. The numerical computations were performed using an unsteady Reynoldsaveraged Navier-Stokes scheme. It is found that the (experimentally measured) shock dynamics are generally well replicated by the numerical scheme, especially at relatively low (≈40 Hz) frequencies. However, variations in shock/boundary-layer interaction structure during unsteady shock motion observed in experiments are not always well predicted by the simulation. Significantly, the computations predict variations in shock/boundary-layer interaction size due to shock motion that are much larger and in the opposite sense to the variations observed in experiments. Comparison of the unsteady results from the present study with steady (experimental) results from the literature suggests that unsteady Reynolds-averaged Navier-Stokes code used in the present study models the unsteady shock/boundary-layer interaction behavior as quasi-steady, whereas experiments suggest that it is more genuinely unsteady. Further work developing numerical methods that demonstrate a more realistic sensitivity of shock/boundary-layer interaction structure to unsteady shock motion is required. © 2011 by the American Institute of Aeronautics and Astronautics, Inc. Source

Dagan Y.,Technion - Israel Institute of Technology | Arad E.,Rafael Laboratories | Arad E.,CFD Group | Tambour Y.,Technion - Israel Institute of Technology | Tambour Y.,Columbia University
Proceedings of the Combustion Institute | Year: 2015

Unsteady turbulent spray-flame structures were computationally investigated, employing the same flow configuration used in previous studies for analyzing the structure of gaseous turbulent flames. The presence of a recirculation zone, which is common in jet engine combustion chambers, has a significant role in spray and flame dynamics, diverting the flame in a cyclic motion. Two repetitive developmental stages of flame structures were identified and analyzed. Droplet grouping was found in the vicinity of large vortical structures, and flames surrounding groups of droplets were identified. Backflow of droplets was found to have ligament structures, similar to those found in turbulent shear flow. The local statistics of fuel droplet dispersion is discussed. A new approach is used to investigate the unsteady changes in flame structure by reducing the dimensionality of the problem, revealing low frequency flame repetitive motions, while retaining its turbulent characteristics. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Source

Montomoli F.,University of Cambridge | Montomoli F.,University of Surrey | Naylor E.,University of Cambridge | Naylor E.,Frazer Nash Consultancy | And 3 more authors.
Journal of Propulsion and Power | Year: 2013

This work presents a numerical simulation of a four-stage axial compressor with cantilevered stators and repeating stages. Two simulations have been accomplished, namely, unsteady with sliding plane and steady with mixing plane, over a wide range of operating conditions. The solver is an unsteady Reynolds-averaged Navier-Stokes code with the Spalart-Allmaras turbulent model. It has been found that the greatest effect of unsteadiness is near the end walls. The stall point for the unsteady simulation is 40%closer to the experimental data when compared with the steady one with mixing planes. This is due to the recovery and segregation of the rotor tip vortex near the casing, which has a stabilizing effect in terms of stall limit. The unsteady simulation is able to reproduce total pressure loss experimentally observed near the hub at the stator exit but not found in the steady simulation. A previous experimental campaign suggested this loss was generated by the wakes of upstream inlet guide vanes propagating through the machine. However, this work found that it is generated by the migration of hub leakage flow induced by the incoming rotor wakes. The unsteady simulation shows higher performance at midspan. This has been found to be related to the rotor wake rectification with a 70% inviscid recovery of wake. Source

Dagan Y.,Rafael Laboratories | Dagan Y.,CFD Group | Arad E.,Rafael Laboratories | Arad E.,CFD Group
Journal of Spacecraft and Rockets | Year: 2014

Adetachable missile nose was designed, tested, and implemented in a new missile. This design enables the use of lowdrag supersonic configurations for the major part of the flight, with the application of blunt seekers that are active during the end game. The configuration of the ejected shroud was designed using a novel approach, which included only a small amount of wind-tunnel experiments, coupled with an aerodynamic model produced by computational fluid dynamics. A simulation of flow dynamics, coupled with rigid-body dynamics, was developed and tested. Databases of aerodynamic forces and moments were produced using quasi-steady computations, for hinged and free flight of the shroud, at very demanding conditions of supersonic flight and large angles of attack. These databases were used by rigid-body dynamic simulations, in one- and six-degree-of-freedom modes, in order to predict the shroud's trajectories. Very good agreement with experimental data has been achieved. The present methodology enabled the analysis of hundreds of trajectories at a reasonable computation effort. Copyright © 2013 byYuval Dagan and Eran Arad. Published by the American Institute of Aeronautics and Astronautics, Inc. Source

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