• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1153-1163
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• 2002

A transient analysis on temperatures of fuel and oil in hydraulic and lubrication systems in an aircraft was studied using the finite difference method. Numerical calculation was performed by an explicit method with modified Dufort-Frankel scheme. Among various missions, air superiority mission was considered as a mission model with 20% hot day ambient condition in subsonic region. The ambience of the aircraft was assumed as turbulent flow. Convective heat transfer coefficient were used in calculating heat transfer between the aircraft surface and the ambience. For an aircraft on the ground, an empirical equation represented as a function of free-stream air velocity was used. And the heat transfer coefficient for flat plate turbulent flow suggested by Eckert was employed for in-flight phases. The governing equations used in this analysis are the mass and energy conservation equations on fuel and oils. Here, analysis of fuel and oil temperature in the engine was not carried out. As a result of this analysis, the ground operation phase has shown the highest temperature and the largest rate of temperature increase among overall mission phases. Also, it is shown that fuel flow rate through fuel/oil heat exchanger plays an important role in temperature change of fuel and oil. This analysis could be an important part of studies to ensure thermal stability of the aircraft and can be applicable to thermal design of the aircraft fuel system.

• Journal of Energy Engineering
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• v.12 no.1
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• pp.11-16
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• 2003

A numerical study was performed on the transient fuel temperatures of a military aircraft stationed under non-operating static condition. Numerical calculation was peformed by an explicit method using modified Dufort-Frankel scheme. It was assumed that the non-operating aircraft is subjected to repeated daily cycles of air temperature with the solar radiation and wind speed corresponding to the 1 % hot day ambient condition. And, the aircraft was assumed to be in turbulent flow. The convective heat transfer coefficient for turbulent flow on the flat plate suggested by Eckert was employed to calculate heat transfer between the aircraft surface and the ambience. The energy conservation equation on fuel was used as governing equation for this analysis. As a result of this analysis, the wing tank temperature showed the highest temperature and the largest rate of temperature changes among fuel tanks. The results of this analysis could be used as initial foe] temperatures for analysis of the transient fuel temperatures in various flight missions. Also, this analysis method could be used to analysis and design of an aircraft thermal energy management system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.73-84
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• 2003

A transient analysis on fuel temperatures in an aircraft was studied using the finite difference method. Numerical calculation was performed by an explicit method of modified Dufort-Frankel scheme. Among various missions, close air support mission was considered with 20% hot day ambient condition in subsonic region. The aircraft was assumed to be in turbulent flow. The fuel system model with additional fuel supplies and return concept was considered. As a result of this analysis, the fuel tank temperatures have increased with the increase of the additional fuel supplies. In contrast to tank temperatures, the fuel temperature at the engine inlet has decreased with the increase of additional fuel supplies except in some in-flight phases having high engine fuel flow. From this analysis, the fuel system with the additional fuel supplies and return concept has been shown to be an effective method to decrease the engine inlet fuel temperature. Also, it has been shown that fuel flow rate through fuel/oil heat exchanger is a key factor influencing fuel temperature.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.4
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• pp.379-384
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• 2011

This paper performs numerical prediction of fuel temperature in the fuel tanks of unmanned air vehicles for both ground static non-operating and in flight transient conditions. The calculation is carried out using a modified Dufort-Frankel scheme. For this calculation, it is assumed that a non-operating vehicle on the ground is subjected to repeating daily cycles of ambient temperature with solar radiation and wind under 1%, with a 20% probability of hot day conditions. The energy conservation equation is used as the governing equation to calculate heat transfer between the fuel tank surface and the ambient environment. Results of the present analysis may be used as the estimated initial values of fuel temperatures in a vehicle's fuel tank for the purpose of analyzing transient fuel temperatures during various flight missions. This research also demonstrates that the fuel temperature of the front tank is higher than that of the rear tank, and that the difference between the two temperatures increases in the later phases of flight due to the consumption of fuel.