This paper investigates field emission behavior from the surface of a tip that was prepared from polymer graphite nanocomposites subjected to electrochemical etching. The essence of the tip preparation is to create a membrane of etchant over an electrode metal ring. The graphite rod acts here as an anode and immerses into the membrane filled with alkali etchant. After the etching process, the tip is cleaned and analyzed by Raman spectroscopy, investigating the chemical composition of the tip. The topography information is obtained using the Scanning Electron Microscopy and by Field Emission Microscopy. The evaluation and characterization of field emission behavior is performed at ultra-high vacuum conditions using the Field Emission Microscopy where both the field electron emission pattern projected on the screen and current–voltage characteristics are recorded. The latter is an essential tool that is used both for the imaging of the tip surfaces by electrons that are emitted toward the screen, as well as a tool for measuring current–voltage characteristics that are the input to test field emission orthodoxy.

This paper deals with active methods of flow control, especially synthetic jet flow control. A synthetic jet was used for flow control in the compressor blade cascade to reduce the vortex structure and reduce the value of the loss coefficients. The output slot of the synthetic jet actuator was situated on the side wall on the connecting line of the leading edges of the blades. The direction of the synthetic jet was perpendicular to the main flow. The synthetic jet excitation is more effective and more efficient than a steady blowing or suction, and its great advantage is zero mass flux supplied to, or taken from the main flow. A positive influence of the synthetic jet on the flow field was proved. The flow field was also visualized.

The main emphasis of the paper is placed on the influence of an active method of flow control, as a synthetic jet, on a flow field around a cylinder with an aspect ratio of 1.8. It summarizes the influence of basic factors that affect the design of the synthetic jet actuator, particularly the Strouhal number - nondimensional frequency (F+), Stokes number of the output orifice (St), Reynolds number (Re), momentum coefficient (cμ), and a position of the output orifice of the synthetic jet actuator. The actuator is positioned in front of the boundary layer separation. The principle of flow control with and without amplitude modulation was used in order to generate a lower actuating frequency. An amount of input energy of the actuators that influences the flow filed was measured. A change of lift and drag coefficients was calculated from the measured pressure distribution by the model. The alternatives with and without flow control are compared through the relation of the saved up and added energy.