Droplet Breakup and Evaporation from Unsteady Accelerations in Hypersonic Weather Impacts
Abstract
Next-generation hypersonic weapons are a critical part of our national defense strategy. To be effective, these hypersonic vehiclesmust be capable of flying through adverse weather environments such as dust, rain, and clouds of small ice or water droplets. Theseatmospheric particles alter the aerodynamics of the vehicle and can impact the surface leading to erosion. Predicting these effectsis complicated by the processing of particles through vehicle bow shocks, consisting of complex shock-expansion wave systems. The overall goal of this project is to understand how droplets breakup and evaporate under unsteady acceleration histories found in hypersonic weather interactions. The specific objective is to develop a reduced-order breakup and evaporation model capable of predictingdroplet properties under unsteady acceleration for implementation in fluids simulation codes. Current breakup models do not accountfor acceleration history or evaporation and are not validated at high gas velocities. This project will provide a new theory for droplet breakup, extending our understanding to challenging unsteady, high-speed conditions, using novel experimental methods and diagnostics to measure droplet breakup and evaporation under unsteady accelerations. This project will leverage the highly controlled conditions generated in a shock-tube environment to create a blast-like wave (coupled shock-expansion wave system) acceleration history by means of an unsupported shock wave. This simple, well-controlled acceleration history will provide a fundamental test case analogous to the particle accelerations found in many hypersonic bow shock systems and allow for the detailed study of droplet hydrodynamic instabilities (HIs) and evaporation. The effect of acceleration history on droplet breakup will first be determined in isolationfrom evaporation effects by using low vapor pressure (butanol and water) droplets. The effect of evaporation will then be tested using high vapor pressure (acetone) droplets that will produce significant amounts vapor during breakup. Various droplet sizes (200µm # 2mm) will be studied to determine the effect of breakup time versus rate of change of acceleration. Droplets will be imaged using high-speed Laser Induced Fluorescence (LIF) of the liquid phase, seeded with Rhodamine dye, to measure droplet acceleration and deformation, HI wavelengths and growth rates, and breakup time. For the high evaporation cases, a two-species (rhodamine and acetone) fluorescence diagnostic will be developed to measure both vapor and liquid phases at high spatial resolutions to determine the effect of evaporation on droplet HIs. The experimental results will be used to validate a new unsteady acceleration breakup model, developed based on HI theory and incorporating droplet deformation and unsteady acceleration, nonlinear growth, and evaporation effects to predict droplet breakup and evaporation. The merit of this work lies in providing high-fidelityexperimental data for droplet breakup and evaporation under unsteady accelerations, like those found in hypersonic weather impacts, and in developing a new fundamental understanding of droplet breakup under high-speed unsteady conditions that can be applied to a wider range of problems, such as liquid-fueled detonations. The project will deliver a variable acceleration droplet breakup and evaporation model for implementation in Navy simulation codes (working with our NRL collaborators). The model will make accurate and efficient system-level simulation of hypersonic weather impacts possible, and will enable the development of resilient hypersonic weapons systems. Additionally, this projectwill train students in areas vital to national security and expose them to research opportunities with the Navy laboratories, enhancing the future naval research workforce.Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 11, 2024
- Source ID
- N000142412252
Entities
People
- Jacob McFarland
Organizations
- Office of Naval Research
- Texas Engineering Experiment Station
- United States Navy