Motivation/Rationale:Predicting and improving the thermal response of military protective equipment is critical to advancingNavy and DOD needs in safeguarding the health and effectiveness of our warfighters. For example, inhot environments, thermal management is not simply an issue of comfort, as prolonged exposure toeven moderately elevated temperatures impairs concentration, task completion, and decision making.Such conditions have been reported to reduce the Warfighter’s situational awareness and vigilance,thereby endangering the safety and effectiveness of our warfighters long before more serious physicalinjury such as heat exhaustion and heat stroke occur. Incorporating thermal management considerationsinto helmet design will improve warfighter effectiveness and reduce fatigue and injury.Pursuing better thermal solutions need not involve exotic materials or complicated, active coolingsystems. A more prudent start would focus on how helmet systems interact with one of the Warfighter’snatural cooling mechanisms: perspiration. As the head perspires, evaporation provides cooling. Themoisture-laden air near the head surface is generally transported away from the head by a combinationof natural convection (i.e., flow induced by the body’s thermal plume), diffusion, and ambient wind.Without this transport, the air near the head saturates, and cooling through evaporation ceases. Padbasedsuspension systems beneath a notional helmet shell directly cover or block some fraction of thehead surface, reducing the area on the head that can perspire effectively, and the combination of padsand shell impede the airflow needed to carry the saturated air away from the head and enable continuedcooling. Quantifying the cooling available depending upon design choices made for the suspension –and correlating this performance to key geometric parameters – would enable thermal considerations tobe incorporated as a potential input variable into a multi-faceted design optimization approach. Anapproach that combines performance with multiple types of conventionally accepted loading (blunt,ballistic and blast) along with thermal performance could drive design decisions during equipmentdevelopment or even fielding decisions for modular equipment depending on theater-specificenvironmental and threat conditions.Objective:The objective of this research is to characterize the evaporative cooling available due to perspiration onthe head for a collection of canonical helmet pad configurations and ambient conditions, to determinethe potential for delivering better thermal performance through passive design considerations.Methods and Results:The paper will discuss results from computational simulations of the flow generated about a standingwarfighter without a helmet, and with two helmet pad arrangements. Cases dominated by buoyancydrivennatural convection and by forced convection due to an ambient wind will be presented. Thetransport generated by each combination of geometry and flow conditions will be assessed to determineeach design’s efficiency in facilitating evaporative cooling via perspiration. Conclusions regarding theefficacy of enabling sufficient cooling through passive means will be explored based in the study results,as will options for packaging the observed behavior into design criteria for multi-objective helmet design.

Head Evaporative Cooling From Forced and Natural Convection for Two Helmet-Pad Configurations

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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