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Rapid, Transient, CFD-Based Solver for Human and Vehicle Thermal Signature Prediction

Description:

TECHNOLOGY AREA(S): Ground Sea 

OBJECTIVE: It is desired to develop a rapid, transient, CFD-based solver for human and vehicle thermal signature prediction involving innovations in flow, heat transfer, air humidity, engine exhaust, and thermal signature modeling and simulation. 

DESCRIPTION: Modeling and simulation (M&S) software capable of analyzing human and vehicle thermal signature already exists; however, as it relates to such thermal solvers, various desirable features, such as transient flow field modeling, are lacking. Thermal solvers typically account for the effects of the problem flow fields on surface heat transfer in multiple ways: (1) through the application of constant heat transfer coefficients and spatially-coarse fluid temperatures without the accounting of flow thermal transport, all within one solver such that computational fluid dynamics (CFD) simulations are not required to be used; (2) through the application of constant heat transfer coefficients and spatially-coarse fluid temperatures with the accounting of flow thermal transport among spatially-coarse subdivided regions of a steady-state flow field, all within one solver but requiring a steady-state CFD simulation to be performed beforehand; and (3) through the application of time-varying, spatially-fine heat transfer coefficients and fluid temperatures with the accounting of flow thermal transport among spatially-fine subdivided regions of a transient flow field, requiring co-simulation between a thermal solver and a CFD solver at each time step. For transient flow and thermal problems, methods 1 and 2 generally would not permit accurate transient modeling, but method 3 requires time- and labor-intensive transient co-simulation between two solvers. Therefore, it would be desirable to develop a new method that: (1) like method 1, can be performed using only one solver; (2) like method 2, accounts for the flow thermal transport among the subdivided regions of the flow field; and (3) like method 3, accounts for time-varying, spatially-fine flow temperatures and heat transfer coefficients for a transient problem. For this new, CFD-based method to be “rapid”, there would need to be limits regarding the spatial discretization of the flow fields and the extent to which the flow field physics are rigorously modeled. It would be desirable to allow the software user to control, through setting the value of a solver input parameter, the balance between accuracy of the predicted flow field and simulation time. Ultimately, the new method should: (1) involve turbulence modeling; (2) involve conduction, convection, and radiation modes of heat transfer; (3) be validated using a notional vehicle case study; and (4) be robust. The development of transient CFD-based modeling capability should facilitate the development of transport modeling of air humidity and engine exhaust. Humidity transport modeling would augment solver capabilities related to heating, ventilation, and cooling (HVAC) modeling and human thermal modeling, and engine exhaust transport modeling would augment solver stand-alone capabilities related to thermal signature. 

PHASE I: For phase I, it is expected that a concept of a rapid, transient CFD-based solving method that can be directly integrated into a thermal signature solver be developed. Related to the CFD-based solving method, the following concept information shall be proposed and delivered: (1) a suitable turbulence model; (2) the entire set of governing physical equations, both flow and thermal; (3) the basic numerical / discretization scheme to be used for solving both the flow and thermal equations in one solver; and (4) a final demonstration / feasibility study. 

PHASE II: For phase II, it is expected that the concept proposed in phase I will be fully integrated into a working, transient, thermal signature solver, including a complete graphical user interface (GUI). All concept refinements subsequent to phase I – such as those involving the proposed turbulence model and the numerical / discretization scheme to be used – shall be provided. A study shall be performed involving the prediction of the thermal characteristics of a notional vehicle which is undergoing “cool-down” after a “heat soak”. “Heat soak” describes the application of steady-state thermal conditions, consistent with SAE J1559, to the unmanned vehicle in a laboratory environment with wind, the vehicle powered off, and all hatches / windows shut; “cool-down” refers to the cooling evolution of the interior cabin of the now-manned, idling vehicle, immediately following the “heat soak” and engagement of the HVAC system. The notional vehicle shall possess sufficient complexity such that significant flow velocity and temperature gradients result inside the vehicle cabin and in the underhood region of the vehicle during “cool-down”. The same study shall be performed using a commercial CFD solver. The main metrics for comparing the two studies shall involve: (1) the flow velocity and temperature at points inside the vehicle cabin and near each soldier consistent with SAE J1503; (2) the flow velocity and temperature at key points in the underhood portion of the vehicle; (3) temperature contours of the exterior vehicle surfaces; (4) vehicle thermal signature assuming a uniform background and specific viewing aspects; and (5) temperature and velocity contours of the vehicle interior and exterior flows associated with specified viewing planes. The viewing planes shall involve: (1) a vertical, longitudinal plane bisecting the vehicle; (2) a vertical, transverse plane bisecting the driver and another bisecting the underhood region; and (3) a horizontal plane bisecting the driver and another bisecting the underhood region. The thermal signature of the vehicle model associated with the commercial CFD solver shall be determined by importing the resulting exterior temperature contours into the thermal signature solver, and determining the “delta-T RSS” signature metric for the same background and vehicle aspects. The “basic hot” environment associated with MIL-STD-810 shall be assumed. 

PHASE III: For phase III, the military application involves a stand-alone, rapid, transient, CFD-based solver for human and vehicle thermal signature prediction which can be used to assess requirement compliance associated with typical military vehicle thermal signature requirements. Such requirements would likely be classified, and may involve various backgrounds, times of year, geographical locations, weather patterns and climates, vehicle aspects, etc. The commercial application would be a stand-alone, rapid, transient, CFD-based solver for human and vehicle thermal modeling, with no thermal signature capability. 

REFERENCES: 

1: SAE J1503: "Performance Test for Air-Conditioned, Heated, and Ventilated Off-Road, Self-Propelled Work Machines"

2:  SAE J1559: "Determination of Effect of Solar Heating"

3:  MIL-STD-810: "Department of Defense Test Method Standard, Environmental Engineering Considerations and Laboratory Tests"

KEYWORDS: Heat Transfer, Thermal Signature, Computational Fluid Dynamics, CFD, Modeling And Simulation 

CONTACT(S): 

Nathan Tison 

(586) 282-4603 

nathan.a.tison.civ@mail.mil 

Yeefeng Ruan 

(586) 282-5602 

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