Tag Archives: wave

Shock Diamonds and the F-22

Within the very high speed flows of air in an aircraft’s exhaust, you can set up a series of shock waves and expansion fans as a result of the differences between the pressure of the flow and that of the surrounding air.  When afterburner is engaged, the hot gases and the temperature changes these shocks and expansions cause, result in a diamond pattern forming in the exhaust plume.  In darker conditions, these diamonds are more conspicuous but they are visible even in normal daylight.

These diamond patterns are a function of the flow being symmetrical since most engines have round exhaust nozzles.  This isn’t the case for the F-22, though.  It has flattened nozzles with a pointed profile top and bottom.  This got me wondering what the effect is on the exhaust plume and whether the traditional diamonds are formed or whether the nozzle shape results in a different pattern of shock and expansions as they reflect within the plume.  I decided to dig in to some shots to see what I could find.

I don’t have a lot of F-22 afterburner shots.  While I have shot them a lot taking off, they often take off without afterburner.  Since they have plenty of power and burner use dramatically increases fuel consumption (and the F-22 is not over-endowed with range as it is), there is no point using burner if it isn’t needed.  Air shows are a time when they do give it plenty of burner, so that is the source of the shots.

The result of this is that there is definitely something unusual about the shock patterns.  I include some shots of F-16 and F/A-18 afterburner plumes and the normal shock patterns that create the hotspots known as the diamonds are very obvious and simple in shape.  For the F-22, things are very different with the patterns of hot zones being something more in line with the shape of the nozzle.  The way in which the patterns repeat is more complex than for an axisymmetric nozzle.  There is nothing much to conclude in these observations.  It is just something that appeals to an old aero guy like me.

Friendly Crews

The taxiway at Hyakuri jinks around the shrine and consequently the towers we were on.  This is probably an inconvenience the crews but this didn’t stop them from being friendly.  The kids on the tower next to me waved at the crews and always got a wave back.  I joined in too and waved whether the kids were there or not.  I don’t think I ever failed to get a response!

Stormy Santa Cruz

The Pacific Coast is picturesque at any time.  Add into the mix a decent swell and things start to look really cool.  We took a trip to Santa Cruz while my mum was staying and the waves were larger than we have seen on any of our previous visits.  The waves were running up to the shore and crashing against the rocks in a very dramatic way.  This wasn’t a stormy day.  There was some wind but the sun was out and it was a very pleasant temperature.  However, something out in the ocean was a bit more active and it had driven the big waves towards the shore.

Not only were the waves crashing into the rocks along the shore, they were also crashing into each other.  As one wave hit the shore, it would reflect back out to see.  There it would meet the next wave coming in.  Waves go in phases with times of small waves interspersed with times of big waves.  (An old Navy helicopter pilot friend of mine – used to landing on pitching decks – said they come in sevens.  I don’t know whether this is accurate but it seems about right.)  When a couple of big waves were together, the impact of the reflecting wave on the incoming wave was pretty dramatic with the water shooting vertically in the air.  I can stand and watch waves all day without any trouble.  Each one is slightly different and they are so full of power.  They are mesmerizing.

Are You Waving at Me?

AE7I3496.jpgTail slapping wasn’t the only thing that the humpbacks were doing a lot of. Waving with a flipper was also going on a lot. I don’t know what this means but it is cool to see because it makes it seem like the whales are waving at you. Since they are underwater when they do it and can’t see you, they obviously aren’t bothered by our presence but who cares? It feels like you are being waved at!

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Blowing the Tops Off the Waves

C59F7057.jpgStanding on the shore watching the waves roll in is a very calming place to be. I can spend hours watching the sea if the opportunity arises. While patterns may emerge, every wave is different and the way they move and interact fascinates me. I have written on this blog about some features of waves that I like such as the even colors when the light shines through the wave just before it breaks. Another feature that can be totally cool is if the wind is blowing offshore.

C59F7068.jpgAs the waves come in and start to break, the wind is rushing up the front side of the wave. The spray that comes off the top of the wave as it breaks gets picked up by this wind and thrown back up and over the wave in the direction from which it has just come. This is a very dynamic effect and watching it is easier than showing it in still form. However, it is still worth a shot and some of these shots give you an idea of the cool spray patterns that result.

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Waves at Santa Cruz

wpid12773-AU0E4796.jpgWhile watching the surfers at Santa Cruz, I also was watching the waves. Photographing waves is immensely frustrating. You see a wave do something really cool and want to get a picture of that. However, the waves never do the same thing twice so you are constantly frustrated. However, I did focus on two aspects of the waves while there. The sun angle was behind the waves so, as they started to break, the light would shine through from behind making a lovely green color light up the water. I find this really attractive and often look for it while watching the sea.wpid12677-AU0E4492.jpg

The other interesting aspect is the way the water runs off the sand after the wave has run its course. The gentle undulations in the surface cause the most interesting patterns to develop. The water is coming from multiple directions so the interaction of the flows results in some fascinating shapes. Looking down on these from above, they become quite abstract.

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