Control of supersonic fluid flow in ducts

Claim 1

A DUCT WITH AN OPEN INTAKE END, FOR USE IMMERSED IN A GAS FLOWING LENGTHWISE OVER THE OUTSIDE OF THE INTAKE END OF THE DUCT A SUPERSONIC RELATIVE VELOCITY, THE DUCT HAVING AN OPENING THROUGH THE WALL THEREOF SUBSTANTIALLY AT THE LOCATION AT WHICH A STOCK WAVE IS TO BE MAINTAINED WITHIN THE DUCT, TOGETHER WITH AN IMPACT PRESSURE SENSING HEAD HAVING A TOTAL HEAD PRESSURE SENSING ORIFICE DIRECTED SUBSTANTIALLY IN THE UPSTREAM DIRECTION, ARRANGED TO BETECT THE IMPACT PRESSURE OF THE GAS FLOWING OVER THE OUTSIDE OF THE DUCT AT A POSITION ADJACENT TO AND A SHORT DISTANCE DOWNSTREAM OF THE OPENING, WHERE THE FLOW OF THE GAS WILL BE SO DISTURBED BY GAS FLOWING OUT THROUGH THE OPENING WHEN THE SHOCK WAVE IS LOCATED UPSTREAM OF THE MOST DOWNSTREAM PART OF THE OPENING AS TO CAUSE ITS IMPACT PRESSURE TO CHANGE, AND MEANS RESPONSIVE TO CHANGES IN THE IMPACT PRESSURE SO DETECTED FOR CHANGING THE PRESSURE IN THE DUCT DOWNSTREAM OF THE OPENING IN THE SENSE TO MAKE THE SHOCK WAVE TRAVEL IN THAT DIRECTION ALONG THE DUCT WHICH TENDS TO REDUCE THE CHANGES IN PRESSURE SO DETECTED, SAID OPENING COMPRISING A NOTCH IN THE LIP OF THE INTAKE END OF THE DUCT, SAID NOTCH HAVING A SUBSTANTIAL DIMENSION LENGTHWISE OF THE DUCT.