- Author
-
Lai, M. C.
|
Faeth, G. M.
- Title
- Structure of Adiabatic Wall Plumes.
- Coporate
- Pennsylvania State Univ., University Park
- Sponsor
- National Bureau of Standards, Gaithersburg, MD
- Report
-
NBS GCR 86-503,
March 1986,
103 p.
- Distribution
- Available from National Technical Information Service
- Contract
- NBS-GRANT-60NANB4D0032
- Keywords
-
buoyancy
|
cross correlation
|
compartment fires
|
laser Doppler anemometry
|
fire research
|
plumes
|
turbulence
|
walls
|
cross correlation
- Abstract
- A theoretical and experimental study of turbulent buoyant plumes along plane surfaces is described. These flows are of interest since their hydrodynamic properties are similar to wall fires and they can be studied withoug complications due to combustion and radiation. Wall plumes were generated by carbon dioxide/air mixtures flowing from a slot at the top of the wall (since the flows were negatively buoyant). Maximum density variations were less than 4%; therefore, the flows were weakly buoyant. The following measurements were made; mean and fluctuating velocities and Reynolds stresses, using laser Doppler anemometry (LDA); mean fluctuating concentrations, using laser-induced fluorescence (LIF); and velocity/concentrtion correlations, using combined LDA/LIF. The flows were also analyzed using a mixing-length model and a k-epsilon-g turbulence model (both ignoring buoyancy/turbulence interactions). Buoyance/turbulence interactions were significant in the present flows; therefore, while predictions of mean properties were reasonably good, turbulence quantities were underestimated. The models were not capable of describing other aspects of the flow as well, e.g., anisotropy of turbulence properties, lack of coincidence of the velocity maximum and the zero Reynolds stress point, and variability of the turbulent Prandtl/Schmidt number. Cross correlations were found which provide a means of estimating differences between Reynolds and Favre-averages, effects of buoyancy/turbulence interactions, and effects of turbulent fluxes on conserved quantities. The results also suggest that the clipped-Gaussian distribution is a reasonable approximation for the probability density function of mixture fraction in wall plumes.