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In the next picture can be seen within the housing, near the inlet:

Front view of turbofan engine Closeup of inlet section enter image description here

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    $\begingroup$ Are those definitely holes and not rivets? Also what are "aerodynamic takes"? $\endgroup$ – Jamiec♦ Oct 29 '15 at 17:21
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    $\begingroup$ My first reaction is rivets, comparing them to the rivets on the seam to the right. The circled ones do look a bit randomly spaced for rivets, though. I'm wondering if it might be the textured surface of the acoustic liner. Hopefully someone that knows for sure will answer. $\endgroup$ – TomMcW Oct 29 '15 at 18:58
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    $\begingroup$ Rivets doesn't appear always evenly spaced or aligned. $\endgroup$ – mins Oct 29 '15 at 21:17
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    $\begingroup$ It is very possible that they're holes too. For example in CF34-10E5 engine the nacelle inlet is full of small holes. Unfortunately I have no idea what they are there for. $\endgroup$ – Sami Oct 29 '15 at 21:36
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    $\begingroup$ @Sami the many small holes further downstream in the inlet serve to reduce the noise. $\endgroup$ – fooot♦ Oct 29 '15 at 21:46
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These are "acoustic liners"; they allow the sound waves to get "trapped" in the holes and make the engine quieter. Sometimes chunks tear loose and they're repaired with what amounts to Bondo.

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  • $\begingroup$ So it's like a silencer for jet engine hah, pretty cool $\endgroup$ – Ali Erdem Mar 5 '19 at 5:05
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This is anti-ice system. Hot air is blown in this holes and ice/snow not settle in jet engine.

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  • $\begingroup$ Welcome. Can you provide a reference to this? $\endgroup$ – mins Oct 31 '15 at 9:22
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    $\begingroup$ No. The silver cowling is heated for anti-icing. These holes aren't for heating, but as @fooot commented above, for noise reduction. $\endgroup$ – Ralph J Oct 31 '15 at 11:45
  • $\begingroup$ This answer is wrong. $\endgroup$ – Scott Baker Jan 28 '19 at 17:06
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The holes you are referring to are a part of the engine-inlet anti-icing system. These holes prevent ice accumulation around the engine inlets. Without them, the engines may ingest ice and will also encounter airflow problems. Engines require laminar airflow in order to operate efficiently.

enter image description here

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    $\begingroup$ Respectfully, your answer is incorrect. $\endgroup$ – Scott Baker Jan 28 '19 at 17:06

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