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AHPCRC Bulletin: Winter/Spring 1996 - Volume 6 Number 1-2

Army and Air Force Researchers Meet at AHPCRC to Discuss Collaboration on Paratrooper Deployment Modeling

Keith Stein (Natick RDEC)

A meeting between researchers from the AHPCRC, the Army and the Air Force took place at the AHPCRC on March 5-6, 1996 to initiate a collaborative effort to exchange information on modeling techniques for predicting the flow fields and multi-body dynamics for paratroopers jumping from tactical aircraft. Army participants included representatives from the Army Research Laboratory (ARL) and the Army Natick Research, Development and Engineering Center (RDEC). Air Force participants included representatives from Wright Laboratory (WL), Arnold Engineering and Development Center, and the Air Force Office of Scientific Research (AFOSR).

The initial paratrooper deployment modeling effort of the Army was established in the summer of 1995 as a collaborative effort between the AHPCRC, ARL, and Natick RDEC. This effort was initiated because it addressed some of the airdrop modeling needs at Natick and also represented the type of problem that the AHPCRC was established to address through collaborative efforts with the Army. Initial test simulations have been performed by Andrew Johnson, a Research Assistant Professor in the AHPCRC research group of Tayfun Tezduyar. Johnson devoted much of the work in his Ph.D. thesis in Aerospace Engineering and Mechanics at the University of Minnesota (UM) to multi-body CFD simulations, unstructured mesh generation, and mesh moving algorithms. For this reason, the initial test simulation produced results in a short period of time. Figure 1 shows the solution at a specific time for the initial fully-coupled multi-body simulation of a paratrooper exiting a delivery aircraft. This simulation was carried out on the CRAY T3D. The simulation required periodic remeshing of the computational domain and used unstructured tetrahedral meshes of approximately 900,000 elements.


Figure 1. Preliminary Aircraft/Paratrooper Interaction Multi-Body Simulation performed at the AHPCRC.
The March 5-6 meetings were scheduled to exchange information regarding paratrooper deployment modeling and to subsequently improve the tools and capabilities for such modeling efforts. The meetings consisted of presentations by some of the participants and discussions on how the different groups could collaborate in future modeling. Following welcoming remarks and introductions by Walter Sturek (ARL) and Tezduyar, presentations were given by Keith Stein (Natick RDEC), Joe Manter and John Nelson (WL), and William Garrard (UM), Vinay Kalro (AHPCRC-UM) and Johnson. Stein gave an overview of the airdrop interests and modeling efforts at Natick. The Mobility Directorate at Natick is currently devoting much attention to modeling the initial deployment of personnel and cargo from delivery aircraft.

Manter is the Head of the CFD Branch which is in the Aeromechanics Division of the Flight Dynamics Directorate at WrightLaboratory. Manter presented an overview of the mission and capabilities of the Aeromechanics Division, focusing on the capabilities within the CFD Research Branch. Figure 2 shows the computed CFD flow fields about two typical delivery aircraft at paratrooper exit conditions. These simulations were performed by a team from WL and NASA Ames Research Center at the request of a joint Army/Air Force Executive Independent Review Team and include work sponsored by AFOSR on adaptively refined cartesian grids.


Figure 2. Inviscid simulations of the flow fields for two typical delivery aircraft at paratrooper exit conditions. (Performed by Wright Laboratory and NASA Ames personnel at the request of a joint Army/Air Force Executive Review Team.)
Nelson gave a more detailed description of the CFD efforts at WL and laid down a set of ground rules that would be necessary in order for WL to be involved in a collaborative effort. In recent years, WL has devoted much effort to the development of capable CFD tools in order to provide better understanding of physical mechanisms and to provide analysis at significant cost savings over purely empirical methods. WL has directed its efforts to both structured and unstructured grid generation and flow solving technology as well as towards the post processing of CFD solutions. WL also has directed efforts to moving technology in addressing store separation problems. Nelson stated that the motivation of WL in participating in a collaborative effort is that the parties involved could learn more about the grid generation, flow solution, and mesh movement aspects of this type of modeling effort. In the future, WL would be interested in addressing the issues of mesh adaptivity and error estimation.

AHPCRC airdrop modeling efforts were presented by Garrard, Kalro, and Johnson. Garrard and Kalro presented the AHPCRC ram air parachute simulations. Kalro addressed the high performance computing aspects of the simulations and Garrard discussed the simple engineering tools that can result from such simulations. Johnson gave a presentation on AHPCRC capabilities for paratrooper deployment modeling. He reviewed the AHPCRC capabilities in space-time formulations for CFD using finite elements, implementations on parallel computers, multi-body CFD simulations, and unstructured surface and volume mesh generation. Johnson stated that future AHPCRC efforts should incorporate more accurate aircraft models with proper flap configurations, boundary layer modeling, and a more refined computational mesh. The desired outcome of the remainder of the meetings were to discuss what information could be exchanged and what collaboration could take place in order to improve current modeling capabilities.

Following the discussions, based on the presentations and discussions, Sturek prepared an unofficial statement for a proposed collaboration on CFD techniques for paratrooper/multi-body modeling. The purpose of the draft memorandum was to outline a proposed collaboration between Army and Air Force research organizations to exchange information on CFD modeling techniques for predicting the flow fields and multi-body dynamics for the deployment of paratroopers from tactical aircraft.