NATIONAL INSTITUTE OF AEROSPACE

Sriram Rallabhandi

Sriram Rallabhandi

Tel: +1 (757) 864-9554; FAX: +1 (757) 864-6306rallabhandi_sriram_bg

Email: sriram.rallabhandi@nianet.org

Research Interests

  • Aircraft Design.
  • Sonic Boom Modeling.
  • Multi-Disciplinary Design Optimization.
  • Aerodynamic Analysis.
  • Computational Fluid Dynamics.
  • Reduced Order Modeling and Model Order Reduction.

Current Research

  • Development of adjoint-based methods for the design of supersonic aircraft for minimizing ground objectives: The goal of this project is to develop a comprehensive methodology for adjoint-based optimization of aircraft concepts for the purpose of reducing the sonic boom generally associated with supersonic flight. Recent advancements include the development of an adjoint formulation of boom propagation to the ground, which provides a framework for generating efficient and discretely consistent sensitivity analysis for optimizing boom metrics on the ground. When coupled with the FUN3D adjoint process, the architecture allows efficient aerodynamic shape optimization. The methodology can be applied to design concepts for under-track and off-track sonic boom minimization and is amenable to massively parallel computing environments through the use of state-of-the-art CFD techniques. This study is conducted in collaboration with the FUN3D development group at NASA LaRC. The current focus of this research is to apply this adjoint-based optimization capability to multi-point design optimization with relevant constraints and other practical considerations. Future work will include consideration of the powered-on engine simulation as well as looking into methods that simultaneously design and adapt the mesh. In addition, this framework may be extended to be coupled with other CFD tools such as CART3D.
  • Development of adjoint-based methods for the design of supersonic aircraft using reversed equivalent areas: The focus of this work is the development, formulation and demonstration of an adjoint-based inverse design process for off-body pressure tailoring for the specific purpose of minimizing the boom of a supersonic concept. The new inverse design process uses the reverse propagation of the pressure distribution (dp/p) from a midfield location to a near-field location and converts the near-field dp/p into an equivalent-area distribution. The reversed equivalent area (Ae,r) is a more accurate approximation of the aircraft than the Ae that is defined by the far-field Mach angle cut method. If Ae,r has a fully shaped low-boom ground signature, so then does the corresponding configuration when the analysis is performed using CFD midfield pressure distributions. The reverse propagation of the pressure distribution using the augmented Burgers equation is developed and verified. A discrete-adjoint version of the reverse propagation is developed. The inverse design method uses Ae,r in a mixed-fidelity low-boom design process to develop low-boom supersonic configurations. A low-boom target for Ae,r corresponds to a low-boom target for the midfield pressure distribution. A gradient-based optimizer attempts to match the Ae,r of a configuration to a prescribed target, thus allowing the designer to generate a low-boom supersonic configuration with a shaped ground signature. Collaborators: Wu Li (NASA Langley)
  • Advanced sonic boom propagation effects: Sonic boom propagation from the aircraft altitude to the ground has traditionally been carried out using linearized physics with cumulative non-linear corrections. However, this fails to capture the other effects, such as thermo-viscous absorption and molecular relaxation during propagation. In the absence of these effects, the predicted ground signature lacks vital information such as shock rise times, resulting in incorrect frequency content. Another aspect to this boom propagation is the effect of atmospheric turbulence and aircraft maneuvers on the sonic boom signature causing ripples and focusing. This research aims to use advanced schemes in the propagation process to predict the sonic boom ground signatures.

Recent Publications

  • Li, W., Rallabhandi, S.K., “Inverse Design of Low-Boom Supersonic Concepts Using Reversed Equivalent-Area Targets”, Submitted for publication in the AIAA Journal of Aircraft
  • Rallabhandi, S.K., “Advanced Sonic Boom Prediction Using the Augmented Burgers Equation”, Journal of Aircraft, Vol. 48, No. 4, pp: 1245-1253
  • Rallabhandi, S.K., Mavris, D.N., “Simultaneous Airframe and Propulsion Cycle Optimization for Supersonic Aircraft Design”, Journal of Aircraft, Vol. 45, No. 1, pp: 38-55.
  • Rallabhandi, S.K., Mavris, D.N., “New Computational Procedure for Incorporating CFD into Sonic Boom Prediction”, Journal of Aircraft, Vol. 44, No.6, pp: 1964-1971
  • Rallabhandi, S.K., Mavris, D.N., “Aircraft Geometry Design and Optimization for Sonic Boom Reduction”, Journal of Aircraft, Vol. 44, No.1, 2007, pp: 35-47
  • Rallabhandi, S.K., Mavris, D.N., “Sonic Boom Minimization Using Inverse Design and Probabilistic Acoustic Propagation”, Journal of Aircraft, Vol. 43, No.6, 2006, pp:1815-1829
  • Utturwar, A., Rallabhandi, S., Delaurentis, D., Mavris, D., “A two-step Optimization Approach for Technology Selection”, Engineering Optimization, Vol. 38, No. 8, December 2006, pp:889:908
  • Rallabhandi, S.K., Nielsen, E. J., Diskin, B., “Sonic Boom Mitigation Through Aircraft Design and Adjoint Methodology”, To be presented at the 30th AIAA Applied Aerodynamics Conference, New Orleans, LA, Jun, 2012
  • Rallabhandi, S.K., “Sonic Boom Adjoint Methodology and its Applications (Invited)”, Presented at the 29th AIAA Applied Aerodynamics Conference, Honolulu, HI, Jun, 2011
  • Li, W., Rallabhandi, S.K., “Inverse Design of Low-Boom Supersonic Concepts Using Reversed Equivalent-Area Targets (Invited)”, Presented at the 29th AIAA Applied Aerodynamics Conference, Honolulu, HI, Jun, 2011
  • Rallabhandi, S.K., “Advanced Sonic Boom Prediction Using the Augmented Burgers Equation”, Presented at the 49th AIAA Aerospace Sciences Meeting, Orlando, FL, Jan, 2011
  • Rallabhandi, S.K., Li, W., Geiselhart, K., “Boom Constrained Drag Minimization for Design of Supersonic Concepts”, Presented at the 48th AIAA Aerospace Sciences Meeting and Exhibit, Orlando FL, Jan, 2010
  • Ordaz, I., Rallabhandi, S.K., “Low Boom -Low Drag Global Shape Optimization Using CART3D”, Presented at the 48th AIAA Aerospace Sciences Meeting and Exhibit, Orlando FL, Jan 2010
  • Plotkin, K.J., Rallabhandi, S.K., Li, W., “Generalized Formulation and Extension of Sonic Boom Minimization Theory for Front and Aft Shaping”, Presented at the 47th AIAA Aerospace Sciences Meeting and Exhibit, Orlando FL, Jan 2009
  • Rallabhandi, S.K., Mavris, D.N., “Simultaneous Airframe and Propulsion Cycle Optimization for Supersonic Aircraft Design”, Presented at the 46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, Jan 2008
  • Lee, K., Rallabhandi, S.K., Mavris, D.N., “Aerodynamic Model Reduction via Probabilistic Principal Component Analysis”, Presented at the 46th  AIAA Aerospace Sciences Meeting and Exhibit, Reno NV, Jan 2008
  • Rallabhandi, S.K., Mavris, D.N., “A New Computational Procedure for Incorporating CFD into Sonic Boom Prediction”, Presented at the 24th  AIAA Applied Aerodynamics Conference, San Francisco, California, June 5-8, 2006
  • Rallabhandi, S.K., Mavris, D.N., “Sonic Boom Minimization Using Improved Linearized Tools and Probabilistic Propagation”, AIAA-2005-1019 Proceedings of the 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, Jan. 10-13, 2005

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