Transition of the Natural Convection Boundary Layer Along a Vertical Heated Wall; Natural Convection in Cavities
h44:
Natural convection in a differentially heated cavity has been paid attention to for a long time, and numerous results
have been obtained. Based on previous studies, the aim of this project is at the enhancement of the heat transfer
through the thermal boundary layer along a vertical heated wall by placing a fin on the sidewall. Numerical simulations
are based on the corresponding flow visualization experiments and focus on the transient natural convection in the
cavity with a fin on the sidewall. The results obtained have demonstrated that the fin significantly impacts on the
transient natural convection flows in the cavity and the enhancement of heat transfer is dependent on the geometric
parameters of the fin such as the position and dimension of the fin. For the purpose of testing the effect of the fin
parameters, many computing cases will be performed and a great deal of computing time and resources will be required for
this project.
f67:
The aim of this project is to understand the transient flow response to periodic thermal forcing in reservoir sidearms
and attics. Relevant to this aim, the associated flow instabilities and their implications to the mixing in reservoirs
or the heat transfer through the attics will also be investigated. The understanding of the fluid dynamics in reservoirs
and lakes is important for determining the quality of water supply. This is because the transport of water properties
depends on the flow conditions. There are a number of processes that promote mixing in reservoirs. Among them, the
horizontal exchange flow induced by unequal heating or cooling is of great interest, and will be one of the focuses of
the present project. On the other hand, the attic space problem has direct relevance to people’s daily life. The
prediction of the heat transfer through the attics is important for building and air-conditioning design. It is also
expected that the understanding of the flow response and heat transfer in attics will eventually lead to finding ways to
control the heat transfer through the attics.
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Principal Investigator Chengwang LeiSchool of Engineering James Cook University |
Project h44, f67 |
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Co-Investigators Feng XuSuvash Saha John Patterson School of Engineering James Cook University |
RFCD Codes 291801, 291802, 291803 |
Significant Achievements, Anticipated Outcomes and Future Work
h44:
The efficiency (speedup) of the parallel computing using Fluent 6.2 for different cases was re-evaluated due to the
hardware change of the APAC machines from SC to AC. The test results show that the best speedup can be achieved with 4
CPUs for most of cases computed in this project. Numerical simulations of natural convection in a differentially heated
cavity with a fin on the sidewall were then performed using FLUENT parallel processes. The results of numerical
simulations have been compared with the corresponding experiments. Both numerical and experimental results have
demonstrated that the fin changes the transient natural convection flows in the cavity and heat transfer. Particularly
in the early stage of sudden heating, a lower intrusion front induced by the fin is formed. Since the lower intrusion
significantly provokes the downstream thermal boundary layer, convection in the downstream is enforced and the heat
transfer there is significantly enhanced, which is supported by corresponding flow visualization. The present project
will be continued, and the effect of the fin parameters on the flow and heat transfer will be the focus of the project
in the next stage. A series of numerical simulations are being planned for the current year to test the effects of the
fin parameters including the position, size, and number of the fin. Further numerical results will also be compared with
corresponding experiments.
f67:
The efficiency of parallel computing using Fluent 6.2 software for the attic problem was evaluated, and it is found that
the best speedup can be achieved with 4~8 Fluent parallel processes, depending on the geometry of the attic. Numerical
simulations of natural convection in attics subject to periodic thermal forcing are then conducted using Fluent parallel
processes. The simulations have revealed many interesting results in terms of flow response and heat transfer. It is
found that the flow response and heat transfer depends strongly on the aspect ratio and Grashof number. Both symmetric
and asymmetric solutions have been obtained in isosceles triangular domains from the present investigation, and the
mechanism responsible for the transition from symmetric to asymmetric structures is being investigated. This work will
be extended in the current year to include the radiation effect in the enclosures. Furthermore, natural convection in
reservoir sidearms subject to periodic thermal forcing will also be investigated numerically in the next stage.
Computational Techniques Used
All numerical simulations were accomplished using the Fluent 6.2 software on the APAC National Facilities Alpha machines (AC). The governing equations (Navier-Stokes and energy equations) are solved using the SIMPLE scheme, which uses a second-order upwind scheme to approximate the advection term and a second-order central difference scheme to approximate the diffusion term. In order to accurately capture the features of the boundary layer flows, a non-uniform grid system was created with concentrated grids in the vicinity of all wall boundaries. Time marching was done by a second order implicit scheme.
Publications, Awards and External Funding
External Funding and Awards
ARC Discovery Project (DP0451679) Natural convection induced exchange flows between near shore and central regions of reservoirs Lei and Patterson
Publications