Effect of initial acceleration on the development of the flow field of an airfoil pitching at constant rate

We present results from a series of experiments where an airfoil is pitched at constant rate from 0 to 60 degrees angle of attack. It is well documented that the dynamic stall behavior of such an airfoil strongly depends on the nondimensional pitch rate K = dot-alpha C/(2U(sub infinity)), where C is the chord, dot-alpha the constant pitch rate, and U(sub infinity) the free stream speed. In reality, the actual motion of the airfoil deviates from the ideal ramp due to the finite acceleration and deceleration periods imposed by the damping of drive system and response characteristics of the airfoil. It is possible that the pitch rate alone may not suffice in describing the flow and that the details of the motion trajectory before achieving a desired constant pitch rate may also affect the processes involved in the dynamic stall phenomenon. The effects of acceleration and deceleration periods are investigated by systematically varing the acceleration magnitude and its duration through the initial acceleration phase to constant pitch rate. The magnitude and duration of deceleration needed to bring the airfoil motion to rest is similarly controlled

Cell Lineages and Genes

Fixed lineages are the extreme manifestation of the interrelations between cell division pattern, spatial organization and cell differentiation occurring in embryonic development. These relationships are discussed in the light of recent new detailed descriptions of lineages, experimental perturbations and genetic analysis. Lineages could be phylogenetically old devices under the control of specific genes that are required to organize the morphological space. Such genes would be different from those involved in the specification of lineage alternatives. Specification genes operate independently from each other and are expressed in a combinatorial way in different cells and lineages. Since their activity is reversible during development the possibility exists for changing these combinatorial associations during development and evolution. The classical notion of a hierarchical cascade segregation of histotypes along lineages is discussed.Peer reviewe

A Conservative Coupling of Level-Set, Volume-of-Fluid and Other Conserved Quantities

© Springer International Publishing Switzerland 2014. A conservative level-set volume-of-fluid synchronization strategy including coupling to other conserved quantities such as mass or momentum is presented. The scheme avoids mass loss/gain of fluidic structures in zero Mach number two-phase flowwhile keeping the interface between the two fluid phases sharp. Local level-set correction and a consistent discretization error control using information from the energy equation based divergence constraint allow for application of the presented method to both constant and variable density zeroMach number two-phase flow with or without interfacial mass transport