Analysis of the flow and thermal fields in bobtail roofs heated from the base wall

Abstract EN

Analysis of airflow and thermal characteristics of attics of bobtail-shaped pitched roofs heated through a horizontally suspended ceiling is numerically carried out in this study.

pitch angles of 14°, 18°, 30°, and 45° within the standard pitch roof range are selected.

the configuration falls within rayleigh number 3.19  105 ≤ Ra ≤ 2.04  107.

a finite-volume CFD code was used to solve the mass, momentum, and energy conservation equations governing the problem.

the results obtained indicate a strong influence on the shape and angle of the roof.

at lower roof pitches, the flow field is characterized by multiple counter-rotating vortices asymmetrically arranged within the enclosures.

eight cells in the 14° enclosure were reduced to five in the 45° roof pitch.

the size and rotating strength of a vortex increase from the left corner to the middle of the enclosures.

at higher pitch angles, the vertical wall obstructed the flow leading to a number of distorted cells.

the maximum velocity within the aerodynamic boundary layer along the base wall occurs at Y = 0.02 with the values U = 0.013 and U = 0.028 in the 14° and 45° enclosures respectively.

the thermal field portrays a convection system of rising hot plumes from the base wall and descending cold jets from the inclined walls ; all enclosed by thin boundary layers along the walls.

graphical plots of velocity and temperature variations along some cross-sections within the enclosures enable the prediction of some important heat and flow parameters.