How accurate are the CFD solutions? Are CFD tools just trend predictors? Then why not just go with an educated guess?

Why put money into say 50K Fluent and not go with a Cosmosfloworks for 10K?

Even a small problem will take a day to run. To complete an optimization it may take weeks to do it.

If you can build and test a prototype in a day then is it worth pursuing a CFD analysis at all?

Wind tunnel testing on a tenth-scale model of an F-15 can run upwards of several hundred thousand dollars/hour of testing. A typical test program can chew up several million dollars. If CFD can shave 20% off the total cost of one test program (and it can) then it's easily paid for itself. CFD solutions are accurate enough to predict drag, determine safe or unsafe separation of equipment from aircraft, and do many other things. Educated guesses are still just that - guesses. And while it may take weeks to run an optimization in cyberspace, do you really think it will be faster in real life, where you have to design and assemble one prototype, test it, analyze and determine what to change, redesign, assemble a new prototype, etc? Which would be cheaper - to cut metal on 10 nozzle designs and run each one over a range of conditions, or grid up 10 nozzles and run the cases on a computer? Is CFD worth it? Even if I didn't work in an area related to CFD, a simple-minded economic analysis of most any real-world situation suggests that it is indeed worth it, provided the tools are wielded by analysts who know how to use them.

1D CFD is _really_ worth it. Combined noise and performance prediction that runs really quick. I know of no OEM or tier 1 automotive company that does not use it.

Can you please provide a list of 1-D cfd code provider?

Professional ethics prevent me from promoting or appearing to promote any particular 1D code, but it can be said that most of the engine engineering consultants market their own in-house codes (Ricardo, AVL, Lotus etc). Plus there are some other suppliers that just sell software (Optimum Power, GT-Power etc). Googling any of these names will lead you to their software pages.

Out of interest, what are you looking to analyse?