Rearward Step (Base Flow)

cfdxue

Recently I have solved rearward step (backward step, base flow) problem. I compare results of TVD, ACM, and Experimental. Just after step, TVD (Yee-Davis) is predicting low pressure ratio (P/Pinf) while ACM44 is predicting very accurate results . But in downstream region both schemes (TVD and ACM44) over predicting pressure ratio.

May you please explain me that:

1. After step, why TVD is predicting low pressure ratio (P/Pinf) while ACM44 is predicting very accurate results???

2. At downstream region, both schemes (TVD and ACM44) over predicting pressure ratio???

Thanks and Regards