Protection of Centrifugal Compressor System

Surge and Choke phenomenon are the two unstable operating modes of a compression system. That surge mode occurs at mass flows below the so-called surge line, and the chock mode occurs at low pressure and high flow rate. These instability operation modes will reduce the compressor performance or even will be made damage to the compressor system [1-3]. There are many studies to prevent instability phenomenon by establishing control system to the ability to do that, but sometimes surge or chock phenomenon occurs although of this big effort. So, for this reason, the paper focus on the protection system, introduced to detect and prevent surge and shock stall occurrence to reduce damages possibility and keep the production at minimum losses. This can be achieved by setting the mass flow rate, pressure ratio, and operating speed in a predefined area. Depending on the data sets including measurements from compression systems of Sirt Oil Company, Libya, and performance characteristics curves and polynomial regression technique to define the operation area. The developed surge protection system was implemented on the Matlab Simulink program and presented in a simple form.

Supersonic Propellers

A start is made by considering why the subsonic propeller was abandoned when aircraft speeds approached the shock stall. It is true that the shock stall also occurs on the propeller blades under these conditions, causing a loss of lift and an increase of drag, but this is not the predominant effect which produces the marked decrease of propeller efficiency associated with high-speed aircraft. The main aerodynamic difficulty associated with the shock stall on the wings of an aircraft is due to the separation of flow caused by the shock wave rather than the presence of the shock wave itself. This difficulty is reduced on a propeller, as any separation of flow which might occur on a propeller blade due to the shock stall, would tend to cause the air to be stagnant relative to the blade, and would thus experience a large centrifugal force by virtue of the propeller rotation. Thus the propeller shock stall would never develop to the same degree that it does on the wings of an aircraft in steady flight.

A Note on the Limitations of Aircraft and Aerofoils used for High Flying Aircraft

The formation of shock waves as a limitation in aircraft design has been considered only, as far as the author knows, in the cases of wing sections at low operating lift coefficients and of the airscrew efficiency. There is, however, a further limitation for high flying aircraft in that the small air density causes the aircraft, even at the stall, to travel at a value of Mach number (V/a) which will cause a shock stall to form on the wing. In some cases the aircraft will be able to prevent this shock stall at high CL by flying faster, but in others, due to high wing loading, the wing sections will be shock stalled at all CL values and the only remedy will be to decrease the wing loading.