TECHNOLOGY AREA(S): Air Platform, Weapons

ACQUISITION PROGRAM: PMA-259 Air-to-Air Missiles

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a physics-based computational approach to predict raindrop distortion and demise in the flow field around a missile in supersonic flight. Conduct laboratory experiments to validate the computational predictions of drop distortion and provide reports on the results.

DESCRIPTION: The ability of a tactical missile to survive flight through rain is likely limited by the ability of its seeker dome to survive flight through rain without fracturing. The biggest unknown in predicting whether the dome will survive in flight is the degree of raindrop distortion caused by the flow field around the missile in flight. The goal of this SBIR topic is to develop a physics-based methodology for prediction of the change in drop shape and to validate predictions with controlled laboratory experiments.

It is expected that the computational approach will require a water equation of state to include supercooling, as droplets in the upper atmosphere can exist in this state. Because drop distortion and eventual drop demise are driven by pressure distributions internal to the drop, the simulations must treat the droplet as a compressible fluid in order to capture time-dependent effects. It is expected that finite element calculations will require a very high resolution with significant grid deformations to capture surface features and shear environment. As the drop surface deforms, surface waves need to be modeled. The effect of water surface tension on the dynamic process will also need to be modeled.

Proposals must demonstrate an understanding of the problem and experience with the methods proposed. A university partner, though not required, could add strength to the research effort.

PHASE I: Develop and demonstrate a physics-based computational method to simulate the distortion of spherical drops in a planar shock front. Evaluate whether the computational method can reproduce shock tunnel drop distortion features observed in Figures 1 and 2 of Reference 5.� Success in Phase I will be evaluated, in part, by the ability to reproduce the observed drop distortion features. Plan a path forward for Phase II that will allow drop distortion to be predicted for the three dimensional flow field around a missile in supersonic flight in the atmosphere. The Phase II proposal should make a convincing case for the realism of the proposed computational approach and for a practical experimental method to validate drop distortion predictions.

PHASE II: Predict the time dependent shape of a drop as it traverses the atmospheric flow field around a missile in supersonic flight. Conduct a parametric computational study for a limited number of representative conditions of speed and altitude with hemispheric and aerodynamic missile forebodies. In consultation with the Government, define and conduct experiments to validate the predictions. Deliver a complete report on the physics behind the computation, material properties used in the computation, and the experimental results used to validate the computation. Develop, deliver, and demonstrate a prototype drop shape calculation computer program capable of being operated by appropriate specialists.

PHASE III DUAL USE APPLICATIONS: Increase the sophistication of the calculations conducted in Phase II for a closer match to observed behavior if required. Conduct new validation experiments as necessary. Improve the interactive characteristics of the software. Transition the technology to appropriate platforms and applications.

It is possible that the results of this work can be applied to predict the ability of commercial rockets to survive launch through some weather conditions.

REFERENCES:

1. Adler, W.F. & Mihora, D.J. �Aerodynamic effects on raindrop impact parameters�. Proc. 5th European Electromagnetic Windows Conf., 1989, Antibes-Juan-Les-Pins, France, pp. 157-164. https://doi.org/10.1016/0043-1648(95)07177-6

2. Adler, W.F. & Mihora, D.J. �Infrared-transmitting window survivability in hydrometeor environments.�� SPIE Proceedings, 1992, Vol. 1760, pp. 291-302.� http://dx.doi.org/10.1117/12.130806

3. Joseph, D.D., Belanger, J. & Beavers, G.S. �Breakup of a liquid suddenly exposed to a high-speed airstream�. International Journal of Multiphase Flow, 1999, Vol. 25, pp. 1263-1303. https://www.aem.umn.edu/people/faculty/joseph/archive/docs/270-JBB.pdf

4. Moylan, B. �Raindrop demise in a high-speed projectile flowfield�. Doctoral Dissertation for the University of Alabama in Huntsville, June 2010.� https://search.proquest.com/openview/33fdb069368fcc15f26a2ed31179401f/1?pq-origsite=gscholar&cbl=18750&diss=y

5. Moylan, B., Landrum, B. & Russell, G. �Investigation of the physical phenomena associated with rain and ice particle impacts on supersonic and hypersonic flight vehicles�.� Procedia Engineering, 2013, Vol. 58, pp. 223-231. http://www.sciencedirect.com/science/article/pii/S1877705813009326

6. Ranger, A. A. & Nicholls, J. A. �Aerodynamic shattering of liquid drops�. AIAA Journal, 1969, Vol. 7, No. 2, pp. 285-290.� https://arc.aiaa.org/doi/abs/10.2514/3.5087

7. Theofanous, T., Li, G., Dinh, T. & Chang, C. �Aerobreakup in disturbed subsonic and supersonic flow fields�. Journal of Fluid Mechanics, 2007, Vol. 593, pp. 131-170. https://doi.org/10.1017/S0022112007008853

8. Wierzba, A. & Takayama, K. �Experimental investigation of the aerodynamic breakup of liquid drops�. AIAA Journal, 1988, Vol. 26, No. 11, pp. 1329-1335.� https://arc.aiaa.org/doi/pdf/10.2514/3.10044

KEYWORDS: Raindrop Distortion; Weather Encounter Analysis; Computational Fluid Dynamics; Hydrocode; Multi-phase Flow; Moving Computational Grids