Abstract:
Computational studies of two- and three-dimensional, turbulent
recirculating flows within mechanically-ventilated enclosures are
reported. Two principal cases are examined: (i) two-dimensional
offset jets: and (ii) three-dimensional flow induced in rooms by
supply jets emanating from low or high side-wall registers. The
calculations were undertaken using iterative finite-domain proceedures
which solve the conservation equations for mass, momentum and
enthalpy, together with additional transport equations for the
turbulent kinetic energy and its dissipation rate . The effect of
buoyancy waS. explicitly accounted for when modelling these equations,
in order that they could be employed to simulate buoyant flow in
ventilated rooms. Computations of the mean velocity, temperature and
convective heat transfer distribution are reported, and compared with
experimental data where available.
A modified version of the two-dimensional elliptic code of Pun
and Spalding (1977) was employed to simulate the offset jet case.
These involve the discharge of a turbulent jet parallel to a flat
surface and eventually attaching to it. The investigations covered a
wide range of offset ratio (3.5-32.4). and the computed flow
properties are compared with measurements from several sources. These
comparisons show good agreement downstream of the reattachment point,
while some discrepancies are evident upstream from this location. The
differences therefore occur mainly in the recirculating flow region,
and are believed to arise from shortcoming in the starting profiles,
the turbulance model and the treatment of the near-wall flow.
A three-dimensional elliptic finite-domain code was developed to
simulate the complex, jet-induced flow within rectangular enclosures.
The code was verified using both laminar and turbulent flow test cases
on simpler geometries. Comparisons with the measurements and
predictions reported by previous researchers were employed for this
purpose. Subsequentlyr the ventilated room simulations were
undertaken using three different ventilation arrangements with thermal
conditions corresponding to isothermall non-buoyant (constant
property) and buoyancy"affected flows. The computations were again
compared with experimental and numerical predictions of previous
researchers. This comparison displayed generally good agreement with
these sources.
A study of the flow and convective heat exchange within a
warm-air heated rom, for which buoyancy effects are significant# is
also reported in a bound paper (Alamdari, Hammonda nd Mohammad, 1986)
for three different heat loads. Its aim to assess the balance between
accuracy and economy provided by the present higher-level method
compared with the intermediate-level convection model of Alamdari and
Hammond (1982) when used to supply building thermal simulation
programs with accurate convection heat transfer data. The computed
results of both models were compared, and indicate that the
intermediate-level is a valuable alternative source that can satisfy
the needs of building thermal modellers. It provides resonable
accuracy at a very modest cost in computing terms.