HIGH REYNOLDS-NUMBER BOUNDARY-LAYER CHAOS

Using tools for the analysis of nonlinear chaotic observations, we hav e determined the embedding dimension required for data from measuremen ts of wall pressure fluctuations in high Reynolds number boundary laye r flow around an axisymmetric body. The Reynolds number based on the b oundary layer size is as large as 10(5), and the number of degrees of freedom excited in the fluid is certainly very large. Yet the active d egrees of freedom seen by the pressure sensors in the transitional and turbulent parts of the flow are as low as 8 to 10. We discuss the sou rce of these results in terms of sensor size and the known coherent st ructures in these shear flows.