******************* This email originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list https://spam.ic.ac.uk/SpamConsole/Senders.aspx to disable email stamping for this address. ******************* Dear All, What could cause the iteration time to increase when halving the time step size? I have a 3-D simulation with an initial CFL 0f about 0.67. Once I halve the time step, the CFL reduces to 0.34 but the iteration time increases! I would expect to have a reduction in the iteration time as well. Thanks syavash