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Flow Simulation-Based Methodology for Reducing The Risk of Fuel Fire In An Aircraft’s Fuel System Enclosure

Janusz Sznajder
Janusz Sznajder
   | 12 jun 2024
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Article Category: research article
Publicado en línea: 12 jun 2024
Páginas: 66 - 92
Recibido: 20 ene 2023
Aceptado: 11 abr 2024
DOI: https://doi.org/10.2478/tar-2024-0012
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© 2024 Janusz Sznajder, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Fig. 1.

Elements of the existing ventilation system of the equipment bay: A-inlet; B,C-front outlets covered with fairings; D,E-rear outlets covered with fairings; F,G – location of two pairs of small drainage holes, invisible in the drawing scale.
Elements of the existing ventilation system of the equipment bay: A-inlet; B,C-front outlets covered with fairings; D,E-rear outlets covered with fairings; F,G – location of two pairs of small drainage holes, invisible in the drawing scale.

Fig. 2.

Space between two last bulkheads of the equipment bay (fuselage skin and cabin floor absent for clarity, view from the rear side). Electric fuel pump on the left, electric battery pack to the right.
Space between two last bulkheads of the equipment bay (fuselage skin and cabin floor absent for clarity, view from the rear side). Electric fuel pump on the left, electric battery pack to the right.

Fig. 3.

Domain included in the model for the external geometry.
Domain included in the model for the external geometry.

Fig. 4.

Domain included in an “intermediate” model.
Domain included in an “intermediate” model.

Fig. 5.

Details of the systems present in the models comprising equipment bay, used for determination of mass flow and pressure values on inlet and outlet surfaces, obtained by 3D scanning (left) and photographed (right).
Details of the systems present in the models comprising equipment bay, used for determination of mass flow and pressure values on inlet and outlet surfaces, obtained by 3D scanning (left) and photographed (right).

Fig. 6.

Boundaries of the equipment bay, view from outside. Positions of surfaces with inlet and outlet boundary conditions indicated by blue and red arrows. Blue dashed ellipse indicates the position of additional inlet used in mesh-independence test.
Boundaries of the equipment bay, view from outside. Positions of surfaces with inlet and outlet boundary conditions indicated by blue and red arrows. Blue dashed ellipse indicates the position of additional inlet used in mesh-independence test.

Fig. 7.

Location of source zone for fuel film (left) and development of the fuel film after approximately 10 seconds (right).
Location of source zone for fuel film (left) and development of the fuel film after approximately 10 seconds (right).

Fig. 8.

Change of film mass in time after start of simulation of fuel film flow.
Change of film mass in time after start of simulation of fuel film flow.

Fig. 9.

Change of phase change rate over time after start of simulation of fuel film flow.
Change of phase change rate over time after start of simulation of fuel film flow.

Fig. 10.

Change of fuel vapor mass over time after start of simulation of fuel film flow.
Change of fuel vapor mass over time after start of simulation of fuel film flow.

Fig. 11.

Change over time in fuel vapor mass trapped inside the bay at decreasing pressure difference between its inlets and outlets.
Change over time in fuel vapor mass trapped inside the bay at decreasing pressure difference between its inlets and outlets.

Fig. 12.

Change over time in fuel vaporization rate at decreasing pressure difference between its inlets and outlets.
Change over time in fuel vaporization rate at decreasing pressure difference between its inlets and outlets.

Fig. 13.

Change over time in fuel vapor outflow mass rate at decreasing pressure difference between its inlets and outlets.
Change over time in fuel vapor outflow mass rate at decreasing pressure difference between its inlets and outlets.

Fig. 14.

Instantaneous transition of stream of fuel droplets (discrete particles) into Eulerian Wall Film at 2 seconds after the start of simulations of the leak. The scale pertains to particle velocity magnitude, while the colours of the fuel film are indicative of wetted fraction of a surface cell. View from front towards the last bulkhead.
Instantaneous transition of stream of fuel droplets (discrete particles) into Eulerian Wall Film at 2 seconds after the start of simulations of the leak. The scale pertains to particle velocity magnitude, while the colours of the fuel film are indicative of wetted fraction of a surface cell. View from front towards the last bulkhead.

Fig. 15.

Change in the film-wetted surface area between t=2s and t=68s of simulation. The view is from the upper front of the bay. For good visibility only the floor and the last bulkhead are shown.
Change in the film-wetted surface area between t=2s and t=68s of simulation. The view is from the upper front of the bay. For good visibility only the floor and the last bulkhead are shown.

Fig. 16.

Distribution of film thickness near outlet holes at t=10s of simulation
Distribution of film thickness near outlet holes at t=10s of simulation

Fig. 17.

Profile of the bottom surface of the equipment bay near the last bulkhead.
Profile of the bottom surface of the equipment bay near the last bulkhead.

Fig. 18.

Changes over time in film mass and mass of fuel vapor inside the equipment bay.
Changes over time in film mass and mass of fuel vapor inside the equipment bay.

Fig. 19.

Cells with fuel vapor concentration above flammability level at t=10s of simulation and at t=68s of simulation.
Cells with fuel vapor concentration above flammability level at t=10s of simulation and at t=68s of simulation.

Fig. 20.

Vectors of velocity in the vertical plane containing the inlet to the equipment bay.
Vectors of velocity in the vertical plane containing the inlet to the equipment bay.

Fig. 21.

Location of additional inlets ventilating the equipment bay.
Location of additional inlets ventilating the equipment bay.

Fig. 22.

Details of the geometry of the additional ventilation inlets.
Details of the geometry of the additional ventilation inlets.

Fig. 23.

View of the additional outlets from the bay and of the filling above the strengthening belt, preventing the accumulation of liquid fuel
View of the additional outlets from the bay and of the filling above the strengthening belt, preventing the accumulation of liquid fuel

Fig. 24.

Fairing for the additional outlets, obtained by scaling of the existing fairing of a small side outlet, visible to the right of the picture (view created using the surface permeability option for visualizing surfaces in ANSYS Design Modeler).
Fairing for the additional outlets, obtained by scaling of the existing fairing of a small side outlet, visible to the right of the picture (view created using the surface permeability option for visualizing surfaces in ANSYS Design Modeler).

Fig. 25.

Contour of velocity stream of fresh air entering the bay through the first additional inlet.
Contour of velocity stream of fresh air entering the bay through the first additional inlet.

Fig. 26.

Contour of velocity stream of fresh air entering the bay through the third additional inlet.
Contour of velocity stream of fresh air entering the bay through the third additional inlet.

Fig. 27.

Time dependence of fluxes of liquid film and fuel vapor, integrated over the surface of all outlets.
Time dependence of fluxes of liquid film and fuel vapor, integrated over the surface of all outlets.

Fig. 28.

Time dependence of mass of fuel film, integrated over the bottom surface, and fuel vapor integrated over the equipment bay volume.
Time dependence of mass of fuel film, integrated over the bottom surface, and fuel vapor integrated over the equipment bay volume.

Fig. 29.

Time dependence of vaporization rate, integrated over the bottom surface.
Time dependence of vaporization rate, integrated over the bottom surface.

Fig. 30.

Distribution of the film thickness after modification of the ventilation system. For good visibility all elements other than wall boundaries of the bay are omitted in the picture, including the fourth bulkhead
Distribution of the film thickness after modification of the ventilation system. For good visibility all elements other than wall boundaries of the bay are omitted in the picture, including the fourth bulkhead

Fig. 31.

Location of cells with mass concentration of fuel vapor above the flammability level. All elements other than wall boundaries omitted in the picture.
Location of cells with mass concentration of fuel vapor above the flammability level. All elements other than wall boundaries omitted in the picture.

Fig. 32.

Time dependence of film mass, integrated over the bay bottom surface, and fuel vapor mass, integrated over the bay volume.
Time dependence of film mass, integrated over the bay bottom surface, and fuel vapor mass, integrated over the bay volume.

Fig. 33.

Time dependence of film mass flow and fuel vapor flow, summed over the outlets.
Time dependence of film mass flow and fuel vapor flow, summed over the outlets.

Fig. 34.

Left: visualization of cells with mass concentration of fuel vapor above the flammability level; right: visualization of cells with mass concentration of fuel vapor above the concentration of 50% of the flammability level. The visualisations were obtained for propeller rpm=481.
Left: visualization of cells with mass concentration of fuel vapor above the flammability level; right: visualization of cells with mass concentration of fuel vapor above the concentration of 50% of the flammability level. The visualisations were obtained for propeller rpm=481.

Fig. 35.

Side view of distribution of cells shown in perspective view in Fig. 27.
Side view of distribution of cells shown in perspective view in Fig. 27.

Pressures on inlet and outlets (relative to operating pressure 101325 Pa) and values of air mass flow.

inlet A outlet C outlet B outlet E outlet D
total pressure [Pa] 164.29
static pressure [Pa] -56.89 -40.03 -57.27 -52.60
air mass flow [kg/s] 3.6124e-2 1.667e-2 1.2259e-2 3.864e-3 3.1346e-3
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