Openside flanker Josh Navidi, outside-half Gareth Davies and wing Richard Smith all come into the team for the BT Sport Arms Park battle.
Rhys Patchell has been switched to full-back and Adam Thomas moves to outside centre after he made his debut in the 33-12 home defeat to Glasgow.Former Pontypridd star Geraint Walsh could make his Blues bow after being selected amongst the substitutes.
Ireland internationals Tommy Bowe and Paddy Jackson come into the Ulster team that sees five changes from their 33-13 defeat of Zebre.Franco van de Merwe joins Dan Tuohy in the second-row and there are also starts for full-back Louis Ludik and centre Stuart Olding.
Ulster are one of four PRO12 sides with an unbeaten record after they backed up their opening day draw at the Scarlets by overcoming Zebre at Ravenhill.But the Blues will be buoyed by their shock 28-23 home victory last season in Dale McIntosh and Paul John’s first game in temporary charge.
Hammett said: “This game will give us another clear indication of exactly where we are as a group and, during what has been a quick turnaround between games, the squad has trained exceptionally hard as we look forward to getting back out on the field.
“In the short period of time I’ve been at Cardiff Blues, it has been pleasing to see that we have assembled a group of players who are prepared to work hard and are eager to learn.We have had to deal with adversity for the first time this season over the last week, but have responded by showing the right attitude and resolve. Now we need to take that mentality and determination over the whitewash and into the Ulster game.
“We have an agreement with the union over Sam Warburton’s availability throughout the season and we have decided to make changes in the back row this week to ensure we get the very best out of him in the long-term while also giving players like Josh Navidi a deserved chance to impress.”
Cardiff Blues: R Patchell, A Cuthbert, A Thomas, GEvans, R Smith, G Davies, L Jones; S Hobbs, M Rees (c), A Jones, J Hoeata, F Paulo, J Turnbull, J Navidi, M Vosawai.
Replacements: R Williams, T Filise, S Andrews, M Cook, E Jenkins, L Williams, C Allen, G Walsh.
Ulster: L Ludik A Trimble, D Cave, S Olding, T Bowe; P Jackson, P Marshall; A Warwick, R Best (c), W Herbst, D Tuohy, F van der Merwe, R Diack, C Henry, N Williams.
Replacements: R Herring, C Black, B Ross, N McComb, R Wilson, M Heaney, I Humphreys, C Gilroy.
