Supersonic airfoil sections:
A supersonic airfoil is a cross-section geometry designed to generate lift efficiently at supersonic speeds. The need for such a design arises when an aircraft is required to operate consistently in the supersonic flight regime. Supersonic airfoils generally have a thin section formed of either angled planes or opposed arcs (called "double wedge airfoils" and "biconvex airfoils" respectively), with very sharp leading and trailing edges. The sharp edges prevent the formation of a detached bow shock in front of the airfoil as it moves through the air. This shape is in contrast to subsonic airfoils, which often have rounded leading edges to reduce flow separation over a wide range of angle of attack. A rounded edge would behave as a blunt body in supersonic flight and thus would form a bow shock, which greatly increases wave drag. The airfoils' thickness, camber, and angle of attack are varied to achieve a design that will cause a slight deviation in the direction of the surrounding airflow. However, since a round leading edge decreases an airfoil's susceptibility to flow separation, a sharp leading edge implies that the airfoil will be more sensitive to changes in angle of attack. Therefore, to increase lift at lower speeds, aircraft that employ supersonic airfoils also use high-lift devices such as leading edge and trailing edge flaps.
Transonic airfoil sections:
The transonic airfoil design problem arises because we wish to limit shock drag losses at a given transonic speed. This effectively limits the minimum pressure coefficient that can be tolerated. Since both lift and thickness reduce (increase in magnitude) the minimum Cp, the transonic design problem is to create an airfoil section with high lift and/or thickness without causing strong shock waves.
One can generally tolerate some supersonic flow without drag increase, so that most sections can operate efficiently as "super critical airfoils".A rule of thumb is that the maximum local Mach numbers should not exceed about 1.2 to 1.3 on a well-designed super critical airfoil.This produces a considerable increase in available Cl compared with entirely sub-critical designs. Super critical sections usually refer to a special type of airfoil that is designed to operate efficiently with substantial regions of supersonic flow.Such sections often take advantage of many of the following design ideas to maximize lift or thickness at a given Mach number:
- Carry as much lift as is practical on the aft potion of the section where the flow is subsonic. The aft lower surface is an obvious candidate for increased loading (more positive Cp), although several considerations discussed below limit the extent to which this approach can be used.
- Make sure that sufficient lift is carried on the forward portion of the upper surface. As the Mach number increases, the pressure peak near the nose is diminished and without additional blunting of the nose, possible extra lift will be lost in this region.
- The lower surface near the nose can also be loaded by reducing the lower surface thickness near the leading edge. This provides both lift and positive pitching moment.
- Shocks on the upper surface near the leading edge produce much less wave drag than shocks aft of the airfoil crest and it is feasible, although not always best, to design sections with forward shocks. Such sections are known as "peaky" airfoils and were used on many transport aircraft.
- The idea of carefully tailoring the section to obtain locally supersonic flow without shock waves (shock-free sections) has been pursued for many years, and such sections have been designed and tested. For most practical cases with a range of design co-efficient of lift and Mach number, sections with weak shocks are favored.
- https://www.highratecpm.com/q2x8d20i? key=9b0eda27ebf376c2939eaffd6689ce7a
