Research statement at the end of my PhD in 2014

Mathematical modeling to predict a physical phenomenon has been playing an important role in the aerodynamic design of ground vehicles or aircrafts. With the advances made recently in high performance computing, the simulations have made it possible to model many complex shapes and environments and completely overshadowed experimental work in many commercial avenues. One of the ways to simulate aerodynamics is to use computational fluid dynamics (CFD) based tools. CFD tools are essentially developed based on first principles to conserve mass, momentum and energy. The set of equations governing the fluid motion and conserving these quantities are also referred in literature to as Navier Stokes (NS) equations. NS equations are a set of non linear partial differential equations. In theory, one can use these equations to solve for any practical problem. However, in order to predict all the scales of motion by using these equations is not possible with the current power of computers. This is mainly due to the different scales of turbulence present in a flow field. One has to then resort to using simplifications that can give reasonably good answers for practical purposes. One such way to use NS equations is to perform ensemble averaging and only allow for mean flow to be predicted. These are referred to as Reynolds Averaged Navier Stokes Equations (RANS). In the RANS framework, a quantitative estimate of turbulence can be achieved by assuming isotropic turbulence assumption and using transport equations to solve for turbulent quantities. My doctorate research contributes to this endeavor of using RANS based modeling to accurately capture the flow physics underneath a hovering rotor operating in ground effect. In what follows, I describe the substance of my doctoral research followed by a few other projects that I recently finished.

Past research:

The motivation of my doctoral research arises from the brownout phenomenon that occurs when helicopters operate in proximity to the ground. The wake from the helicopter rotor interacts with the ground plane and causes the lose sediment particles on the ground to get mobilized. These sediments get entrained in the rotor wake and cause an obstruction to pilot’s field of view along with damaging the expensive blades. This problem is attributed to three fourths of mishaps occurring in Middle East operations. Since the rotor wake interacting with the ground plane is the root cause of this phenomenon, it also gives hope to the researchers that by changing the characteristics of the rotor wake, one can mitigate or prevent brownout. The understanding of rotor wake capturing until it interacts with the ground is a challenging task. This requires the accurate capture of the generation of vorticity on the rotor blade surfaces, including the tip vortex, and the subsequent evolution and rollup into the tip vortices, and the convection and interaction of this vorticity into the developing wall jet and boundary layer on the ground. In order to achieve this goal, a three dimensional structured, curvilinear, compressible, unsteady Reynolds-Averaged based Navier Stokes (RANS) solver, parallelized using MPI, with overset mesh capability was utilized. The turbulent quantities are modeled using a one equation transport model of eddy viscosity also known as Spalart Allamaras Turbulence model. One of the challenges in modeling consists of preserving the rotor generated tip vortices for longer time periods and capturing their interactions with ground. Therefore, various mesh placement strategies were devised to efficiently capture the path of the tip vortices for both regimes. The RANS predictions were further improved for a higher Reynolds number case by improving the turbulence modeling. The results of this work compared well with the experimental data and also suggested that a change in blade design might have a benign effect on reducing the effect of rotor wake impinging on the ground plane. Other than my doctoral research, I have briefly described other projects that were carried upon and published with collaboration from fellow researchers on this webpage. (https://sites.google.com/site/taranskalra/projects)

Future Work:

In most of my doctoral work and other projects, I have primarily used and developed computational tools based on RANS approach. In my future work, I want to develop new computational tools

With the above ideas in mind, my long-term goal is to carry out interdisciplinary research that can utilize my background in fluid mechanics/aerodynamics, scientific computing and engineering to solve real world problems. As a final thought, I am excited to form collaborations with other faculty and industry in order to explore new and challenging methodologies that can solve the issues of aerodynamic design or any other engineering pursuit.

Bibliography:

  1. Kalra, T. S., Lakshminarayan, V.K., Baeder, J.D, ‘Effect of Tip Geometry on a Hovering Rotor in Ground Effect: a Computational Study’, AIAA Summer Conference, San Diego, CA, June 2013
  2. Lakshminarayan, V. K., Kalra, T. S., and Baeder, J. D., ‘Detailed Computational Investigation of a Hovering Microscale Rotor in Ground Effect,’ AIAA Journal, Vol. 51, (4), April 2013, pp. 893-909
  3. Thomas, S., Kalra, T. S., Baeder, J.D., ‘A Hybrid CFD Methodology to Model the Two-phase Flowfield beneath a Hovering Laboratory Scale Rotor’, AIAA Summer Conference, New Orleans, LA, June 2012
  4. Thomas, S., Lakshminarayan, V.K., Kalra, T. S., Baeder, J.D., ‘Eulerian-Lagrangian Analysis of Cloud Evolution using CFD Coupled with a Sediment Tracking Algorithm’, AHS Forum, Virginia Beach, VA, May 2011
  5. Kalra, T. S., Lakshminarayan, V.K., Baeder, J.D., Thomas, S., ‘Methodological Improvements for Computational Study of Hovering Micro-Rotor in Ground Effect’, AIAA Summer Conference, Honululu, Ha, June 2011
  6. Kalra, T. S., Lakshminarayan, V. K., and Baeder, J. D., ‘CFD Validation of Micro Hovering Rotor in Ground Effect,’ American Helicopter Society 66th Annual Forum Proceedings, Phoenix, AZ, May 2010
  7. Rinehart, T., Medida, S., Kalra, T. S., and Baeder, J. D., ‘RANS Simulations of Sandia 100-m Wind Turbine Blade: Effect of Leading-Edge Tubercles’, AIAA Summer Conference, Atlanta, GA, June 2014
  8. Baeder, J.D, Medida. S., Kalra, T. S., ‘Computational Validation of a Hovering S-76 Rotor’, AIAA SciTech Conference, Washington DC, Jan 2014
  9. Thomas, S., ‘A GPU-Accelerated, Hybrid FVM-RANS Methodology For Modeling Rotorcraft Brownout,’ Ph.D. Dissertation, Department of Aerospace Engineering University of Maryland at College Park, 2013