想讓飛機超音速？先去激光屠宰場！從豬肉切片探秘飛機的超音速面積律【沒萌萌戰隊】

most recent flight in the air force A netizen who was a flight attendant sent a private message saying He found that the waist of the J-10 fighter was obviously concave Upon inquiry, I found out that this is a wasp-waist fuselage designed according to the law of area Said to reduce drag What is the reason for this, but I have never figured it out. In fact, it has been 70 years since the area law was born. in the early 1950s Top hurdle in researching supersonic aircraft is the intense compression of the air in front of the plane as it approaches the speed of sound shock wave formation And produce a lot of shock wave resistance and it is difficult to continue to accelerate At that time it was proposed Shock wave drag experienced by an aircraft at zero lift and the cross-sectional area distributed along the longitudinal axis The square of the second derivative is proportional to Listen to what people say Actually he meant the wave resistance of the plane Equivalent rotation body at the same cross-sectional area are approximately equal And it's much easier to study spiral bodies than it is to study airplanes That being the case Let's make the equivalent rotation body of this machine For this we're going to a hog slaughterhouse Here is a tool for killing pigs Will let the old sow be cut into countless thin slices without knowing it So we use this tool to slice the plane from front to back And draw the curve of the cross-sectional area distribution along the vertical axis Then the curve is made Equivalent rotation body with equal cross-sectional area everywhere We were disappointed to see the shape of this rotating body Since the 1940s Sias and Huck discovered through mathematical derivation Rotation body at a given length and volume This shuttle shape is the smallest transonic shock resistance coefficient Sias-Hacke Only let the equivalent of the plane rotate into a body The shape is as close as possible to the Sias-Hack spiral body Transonic drag coefficient can be reduced But the cross-sectional area curve of the ideal spiral Much smoother than the curve of this machine After inspection, it was found that the belly of the plane and the wings were superimposed Causes the local cross-sectional area to be too large to make the curve obviously protrude So I can only lose weight on my stomach A plane that loses its belly becomes a bee-waisted fuselage The curve of the cross-sectional area becomes flatter and close to the ideal curve thereby significantly suppressing transonic drag So this method of modifying drag reduction transonic area law But a new problem arises when the plane exceeds the speed of sound point on the area distribution curve no longer represents the cross-sectional area of ​​the aircraft Rather, it represents the rear Mach cone at the station point on the longitudinal axis and the oblique area of ​​the plane The Mach cone mentioned here refers to Disturbance of the air flow by a tiny object produces weak spherical Mach waves If the airflow is greater than the speed of sound Then the front of the wave will recede relative to the disturbance source Make countless spherical surfaces form a conical envelope So it was named Mach cone after the discoverer The half angle of the cone is called the Mach angle The tangent of this angle is given by the formula It can be seen that when the incoming flow velocity is Mach 1, the Mach angle is 90 degrees So the Mach cone is the oblique area of ​​the disk and the plane is the fuselage cross-sectional area used by the transonic area law When the Mach number increases beyond the speed of sound, the Mach angle decreases. The oblique area between the Mach cone and the plane will change Change the area distribution curve Therefore, let the equivalent of the plane be rotated into a body It is close to the shape of the Sias-Hack spiral body Only for the selected Mach number Mach cone oblique area distribution curve optimization thus reducing the shock drag coefficient at this speed This is called the supersonic area law American YF-23 fighter jet It is a model of supersonic area law optimization It is optimized to reduce Mach 1.5 Wave drag coefficient in flight Also in Sias-Hack rotation Area distribution curve as a reference At an oncoming Mach number of 1 The cross-sectional area distribution curve of the machine changes abruptly Large deviation from the reference curve Therefore, the shock wave resistance coefficient is relatively large at transonic speed But at Mach 1.5 The rear Mach cone at the station point on the longitudinal axis of the fuselage The half top angle is 41.8 degrees The distribution curve of the oblique area with the body I don't know how It magically basically coincides with the reference curve This makes the machine's shock drag coefficient at Mach 1.5 significantly lower Although YF-23 failed But its design allows us to recognize A pig slaughtering workshop must not stop at vertical slices Instead, we should take the customer's requirements as the optimization goal According to the supersonic area law, cut out the conical meat slices