What happens to the air or water flow in front of a craft traveling at a relativley high speed?

Question

I want to know the wake created in front of the craft moving through a medium. Is it a single compression or multiple compressions.

Answer 1

What you are talking about is a bow wave. It forms because the the boat or aircraft forming that wave on its bow is going faster than the medium (air, water) can get out of the way. It's something like pushing on the edge of a rug, the rug bunches up because your push is harder and faster than the rug's material can support.

When the craft is traveling slow enough, the medium can get out of the way as the craft cuts through it. Turns out that air can get out of the way of anything traveling less than the speed of sound. But travel faster than sound and the bow wave (and the sonic boom) will form.

As you might guess, bow waves sap energy from the otherwise kinetic energy propelling the craft. So modern ship's design has incorporated large blunt bows just below the water line. These blunt noses (looking somewhat like the noses of porpoises) help to smooth out the water in front of the ship and, thereby, reduce the bow wave and consequent loss of useful energy.

Bow waves are standing transverse waves on the surface of water. But they start out as compressive waves (and stay that way in air). As standing waves, they consist of harmonic waves that augment or cancel out; depending on the energy (frequencies) making up the waves.

On the surface of water, in front of a large ship travel fast (e.g., an aircraft carrier), one can see several standing bow waves. So there would be commensurate compression waves.

By the way, the word "wake" is reserved from the churning and such following a ship or aircraft, not in front. Bow wave is the proper term for all that in front...off the bow.