i9-9900k for Ansys cfd.

Zaber5 · January 2, 2019, 11:55

I am building a new desktop, mainly for Ansys fluent and some mechanical. My mesh sizes vary between 1mil to 6mil. For my budget I was thinking to buy the new i9-9900k. How well does this CPU perform CFD simulations? Any other CPU recommendations in my price range would be appreciated.

Simbelmynë · January 2, 2019, 12:58

In my country the 9900k is extremely overpriced (approx. 570 Euro). That is approximately the same as the much faster 7820X!

9700k should give the same performance @ 440 Euro (unlikely that the extra L3 cache will yield a significant performance difference).

9600k would also give very similar performance @ 300 Euro and is probably a much better option than the 8700k @ 420 Euro.

As a comparison - My old 7600k yield similar results as the 8700k when I use slightly higher memory clock speeds.

For pre-processing such as meshing, then the 9900k is probably be the best CPU you can get right now.

Zaber5 · January 2, 2019, 13:23

Thanks for the reply. Are you sure the 7820x is faster than 9900k? From the benchmarks I saw online 9900k is slightly faster. I might be wrong.
Also what about the AMD ryzen threadripper series? Especially the 1920x or the 2920x.

Simbelmynë · January 2, 2019, 13:35

The 7820X will be much faster if you use all 8 cores, the 9900k will most likely hit the memory bottleneck when running on more than 4 of the 8 cores.

Threadrippers can be used, but they normally have less room for overclocking. Check the benchmark thread for some comparisons between Threadrippers and 7820X.

Zaber5 · January 2, 2019, 13:42

Thanks! Sorry but could you please explain memory bottleneck in 9900k. I didnt quite understand it. Are you referring to the RAM?

Simbelmynë · January 2, 2019, 13:52

Yes. The 9900k has 2 memory channels. The 7820X has 4 memory channels.

Note that this has nothing to do with the amount of RAM installed, but rather how the CPU can communicate with the memory. The memory bandwidth is a measure of the width of the memory bus as well as the memory speed and the number of memory channels.

flotus1 · January 5, 2019, 13:45

Quote:

Originally Posted by Simbelmynë

Note that this has nothing to do with the amount of RAM installed

I know what you meant, but just to make sure OP makes the right choice: A CPU with 4 memory channels needs 4 physical DIMMs populated in order to leverage the quad-channel memory interface. E.g. 4x8GB or 4x16GB in the correct slots. The motherboard manual holds information about which slots are the right ones.

January 2, 2019, 11:55	i9-9900k for Ansys cfd.	#1
Zaber5 New Member Abhishek Join Date: Dec 2018 Posts: 6 Rep Power: 7	I am building a new desktop, mainly for Ansys fluent and some mechanical. My mesh sizes vary between 1mil to 6mil. For my budget I was thinking to buy the new i9-9900k. How well does this CPU perform CFD simulations? Any other CPU recommendations in my price range would be appreciated.

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January 2, 2019, 12:58		#2
Simbelmynë Senior Member Join Date: May 2012 Posts: 551 Rep Power: 16	In my country the 9900k is extremely overpriced (approx. 570 Euro). That is approximately the same as the much faster 7820X! 9700k should give the same performance @ 440 Euro (unlikely that the extra L3 cache will yield a significant performance difference). 9600k would also give very similar performance @ 300 Euro and is probably a much better option than the 8700k @ 420 Euro. As a comparison - My old 7600k yield similar results as the 8700k when I use slightly higher memory clock speeds. For pre-processing such as meshing, then the 9900k is probably be the best CPU you can get right now.

January 2, 2019, 13:23		#3
Zaber5 New Member Abhishek Join Date: Dec 2018 Posts: 6 Rep Power: 7	Thanks for the reply. Are you sure the 7820x is faster than 9900k? From the benchmarks I saw online 9900k is slightly faster. I might be wrong. Also what about the AMD ryzen threadripper series? Especially the 1920x or the 2920x.

January 2, 2019, 13:35		#4
Simbelmynë Senior Member Join Date: May 2012 Posts: 551 Rep Power: 16	The 7820X will be much faster if you use all 8 cores, the 9900k will most likely hit the memory bottleneck when running on more than 4 of the 8 cores. Threadrippers can be used, but they normally have less room for overclocking. Check the benchmark thread for some comparisons between Threadrippers and 7820X.

January 2, 2019, 13:42		#5
Zaber5 New Member Abhishek Join Date: Dec 2018 Posts: 6 Rep Power: 7	Thanks! Sorry but could you please explain memory bottleneck in 9900k. I didnt quite understand it. Are you referring to the RAM?

January 2, 2019, 13:52		#6
Simbelmynë Senior Member Join Date: May 2012 Posts: 551 Rep Power: 16	Yes. The 9900k has 2 memory channels. The 7820X has 4 memory channels. Note that this has nothing to do with the amount of RAM installed, but rather how the CPU can communicate with the memory. The memory bandwidth is a measure of the width of the memory bus as well as the memory speed and the number of memory channels.