On non-degenerate Berge-Turán problems

Given a hypergraph $\mathcal{H}$ and a graph $G$, we say that $\mathcal{H}$ is a $\mathit{\text{Berge}}$-$G$ if there is a bijection between the hyperedges of $\mathcal{H}$ and the edges of $G$ such that each hyperedge contains its image. We denote by $e{x}_k(n,\text{Berge-}F)$ the largest number of hyperedges in a $k$-uniform Berge-$F$-free graph. Let $ex(n,H,F)$ denote the largest number of copies of $H$ in $n$-vertex $F$-free graphs. It is known that $ex(n,K_k,F)\le e{x}_k(n,\text{Berge-}F)\le ex(n,K_k,F)+ex(n,F)$, thus if $\chi (F)>r$, then $e{x}_k(n,\text{Berge-}F)=(1+o(1))ex(n,K_k,F)$. We conjecture that $e{x}_k(n,\text{Berge-}F)=ex(n,K_k,F)$ in this case. We prove this conjecture in several instances, including the cases $k=3$ and $k=4$. We prove the general bound $e{x}_k(n,\text{Berge-}F)=ex(n,K_k,F)+O(1)$.