(547f) Analysis of Pressure Fluctuations In Fluidized Beds: I. Similarities with Turbulent Flow

Sahimi, M., University of Southern California
Ghasemi, F., University of Minnesota
van Ommen, J. R., Delft University of Technology

Experimental data for pressure fluctuation time series in a fluidized
bed are analyzed by several distinct, but complementary methods. First, we
compute a multiscale probability density function (PDF) for the successive
increments of the data. The results demonstrate the evolution of the PDF from
the short to long time scales, and indicate striking similarity to the Castaing
equation that has been proposed for modeling velocity fluctuations in turbulent
flows. Next, to further check the results we compute the structure function of
the successive increments of the data. We find that the fluctuations exhibit
multifractal behavior, which is also prevalent in turbulence. The
multifractality implies that the pressure fluctuates differently over distinct
time scales. To understand the origin of the multifractality, we use a powerful
method of analysis, namely, the multifractal detrended fluctuation analysis
(MF-DFA) in order to analyze the data. The results confirm the multifractal
property of the data. To better understand the similarities between the
pressure fluctuations in fluidized beds and velocity fluctuations in turbulent
flow, and whether the multifractality is due to extended correlations in the
data or because the PDF of the successive increments is broad, we also
construct the {\it shuffled} and {\it surrogate} series for the data and
analyze them by the MF-DFA method. Comparison of results for the original data
with the shuffled and surrogate time series indicates that the correlations in
the pressure are responsible for the multifractality of the data, rather than
the broadness of the PDF.