Leger T.,U.S. Air force |
Leger T.,Ohio Aerospace Institute |
Bisek N.,U.S. Air force |
Bisek N.,Research Aerospace Engineer |
And 2 more authors.
Journal of Thermophysics and Heat Transfer | Year: 2016
Reynolds-Averaged Navier-Stokes simulations were carried out for sharp fin-induced shock wave/turbulent boundary-layer interactions at Mach 5. Calculations were executed for two fin angles of attack, with each case employing four turbulence models. The computational results were compared with vetted experimental data. For all the cases considered, the calculations replicated the experimentally observed flow structure, which is primarily determined by inviscid, rotational flow effects. Predictions of parameters dominated by viscous effects tended to be less accurate. The predictions of the different turbulence models were qualitatively consistent, but the predicted peak skin friction and wall heat flux varied by as much as a factor of two between the models. The discrepancies between computation and experiment are believed to be a result of large-scale unsteadiness and three dimensionality, which are not captured well by conventional turbulence models. © Copyright 2015 by the American Institute of Aeronautics and Astronautics, Inc.
Reyes D.A.,Texas A&M University |
Reyes D.A.,China Aerospace Science and Technology Corporation |
Girimaji S.S.,Texas A&M University |
Girimaji S.S.,China Aerospace Science and Technology Corporation |
And 3 more authors.
Journal of Aircraft | Year: 2013
Turbulent flow computations of the NASA "trap-wing" high-lift configuration are performed at various angles of attack usinga k-ωfamily ofmodels to assess their capabilities for high-lift design and optimization applications. The four k-ωmodel variants used are: 1)Wilcox's 1988 baseline model; 2) variable-β* model consistentwith the rapidly strained limit; 3) variable-β* model consistent with the explicit algebraic Reynolds stress model; and 4) Wilcox's 2006 enhanced model. Subject to the conditions of this test, the variable-β* model consistent with the rapidly strained limit not only performs the best but is also numericallymore robust and does not require the use of a production-to- dissipation limiter. Overall, our findings indicate that variable β* makes an important difference. In the proximity of stall, a low-Reynoldsnumber correction to eddy viscosity may be needed to accurately capture experimental behavior. The results provide much needed insight into the models' predictive capabilities and identify areas for future k-ω model improvements. © 2012 AIAA.
Chen N.Y.,NASA |
Chen N.Y.,Research Aerospace Engineer |
Sridhar B.,NASA |
Ng H.K.,University of California at Santa Cruz |
Ng H.K.,University Affiliated Research Center
Journal of Aircraft | Year: 2012
This paper describes a class of strategies for reducing persistent contrail formation with the capability of trading off between contrails and aircraft-induced emissions. The concept of contrail-frequency index is defined and used to quantify the contrail activities. The contrail-reduction strategies reduce the contrail-frequency index by altering aircraft's cruising altitude with consideration to extra emissions. The strategies use a user-defined factor to trade off between contrail reduction and extra emissions. The analysis shows that contrails can be reduced with extra emissions and without adding congestion to airspace. For a day with high contrail activities, the results show that the maximal contrail-reduction strategy can achieve a contrail reduction of 88%. When a tradeoff factor is used, the strategy can achieve less contrail reduction while emitting less emissions compared to the maximal contrail-reduction strategy. The user-defined tradeoff factor provides a flexible way to trade off between contrail reduction and extra emissions. Better understanding of the tradeoffs between contrails and emissions and their impact on the climate need to be developed to fully use this class of contrail-reduction strategies. The strategies provide a starting point for developing operational policies to reduce the impact of aviation on climate. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc.
Morris P.J.,Pennsylvania State University |
Miller S.A.E.,NASA |
Miller S.A.E.,Research Aerospace Engineer
AIAA Journal | Year: 2010
Broadband shock-associated noise is a component of jet noise generated by supersonic jets operating offdesign. It is characterized by multiple broadband peaks and dominates the total noise at large angles to the jet downstream axis. A new model is introduced for the prediction of broadband shock-associated noise that uses the solution of the Reynolds-averaged Navier-Stokes equations. The noise model is an acoustic analogy based on the linearized Euler equations. The equivalent source terms depend on the product of the fluctuations associated with the jet's shock-cell structure and the turbulent velocity fluctuations in the jet shear layer. The former are deterministic and are obtained from the Reynolds-averaged Navier-Stokes solution. A statistical model is introduced to describe the properties of the turbulence. Only the geometry and operating conditions of the nozzle need to be known to make noise predictions. This overcomes the limitations and empiricism present in previous broadband shock-associated noise models. Results for various axisymmetric circular nozzles and a rectangular nozzle operating at various conditions are compared with experimental data to validate the model. Copyright © 2010 by Philip J. Morris and Steven A. E. Miller. Published by the American Institute of Aeronautics and Astronautics, Inc.
Kopardekar P.,NASA |
Rios J.,NASA |
Prevot T.,NASA |
Johnson M.,NASA |
And 3 more authors.
16th AIAA Aviation Technology, Integration, and Operations Conference | Year: 2016
Many applications of small Unmanned Aircraft System (UAS) have been envisioned. These include surveillance of key assets such as pipelines, rail, or electric wires, deliveries, search and rescue, traffic monitoring, videography, and precision agriculture. These operations are likely to occur in the same airspace in presence of many static and dynamic constraints such as airports, and high wind areas. Therefore, small UAS, typically 55 lb and below, operations need to be managed to ensure safety and efficiency of operations is maintained. This paper will describe the Concept of Operations (ConOps) for NASA’s UAS Traffic Management (UTM) research initiative. The UTM ConOps is focused on safely enabling large-scale small UAS (sUAS) operations in low altitude airspace. The UTM construct supports large-scale visual line of sight and beyond visual line of sight operations. It is based on two primary mantras: (1) flexibility where possible and structure where necessary (2) a risk-based approach where geographical needs and use case indicate the airspace performance requirements. Preliminary stakeholder feedback and initial UTM tests conducted by NASA show promise of UTM to enable large-scale low altitude UAS operations safely. © 2016 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.
Ricciardi A.P.,Virginia Polytechnic Institute and State University |
Ricciardi A.P.,Ocean Aero |
Canfield R.A.,Virginia Polytechnic Institute and State University |
Canfield R.A.,Ocean Aero |
And 4 more authors.
Journal of Aircraft | Year: 2016
A systematic approach for aeroelastic scaled-model design is developed. The method optimizes an incremental number of vibration eigenpairs, buckling eigenpairs, and optionallya linear static responseof scaled models to match the scaled values of a target full-scale aircraft. A method for matching scaled modal mass, a required scaling parameter, isdeveloped. The sources of local optima are identified and a tiered global-search-optimization procedure is incorporated. The approach is demonstrated on a joined-wing scaled-model-design problem. Costly nonlinear analysis is omitted from the evaluation of the objective function and constraints for optimization. The results produced scaled models that closely replicate the geometrically nonlinear target aeroelastic behavior. Copyright © 2015 by the authors. Published by the American Institute of Aeronautics and Astronautics, Inc.