And as they bid to bring the curtain down on their campaign in Edinburgh on Saturday, they know they can finish no higher than seventh.
But while they aren't able to secure a top-six finish, Turnbull believes the Blues' four victories from six Welsh derbies points to a successful season, and one he is keen to build on next term.
"Last year we struggled to win any derbies but this year we've won four out of six and that's a positive thing. Hopefully we can grow on that again next year," Turnbull told the club's official website.
"With the momentum we've had and the changes we've made, Danny (Wilson) has always said it would be a slow process and people would have to bear with us.
"It was about changing perceptions of what people have had of Cardiff Blues previously and slowly but surely we are doing that.
"Don't expect anything too soon but with the growth we have shown this year, we are moving forward and hopefully we can continue that next season.
"But first we have Edinburgh, they have been going well they are in and around the same position as us - it will be a great game. Both teams will want to go out and throw the ball around."
To buy tickets for the Guinness PRO12 Grand Final click here. Also follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up for our newsletter for regular updates on the Guinness PRO12.
Guinness PRO12 Blues News
63x46.png){kind=logo}