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In many simulations of turbulent flows the viscous forces $\nu\nabla^2 {\bfu}$ are replaced by a hyper-viscous term $-\nu_p(-\nabla^2)^{p}{\bf u}$ inorder to suppress the effect of viscosity at the large scales. In this work weexamine the effect of hyper-viscosity on decaying turbulence for values of $p$ranging from $p=1$ (regular viscosity) up to $p=100$. Our study is based ondirect numerical simulations of the Taylor-Green vortex for resolutions from$512^3$ to $2048^3$. Our results demonstrate that the evolution of the totalenergy $E$ and the energy dissipation $\epsilon$ remain almost unaffected bythe order of the hyper-viscosity used. However, as the order of thehyper-viscosity is increased ,the energy spectrum develops a more pronouncedbottleneck that contaminates the inertial range. At the largest values of $p$examined, the spectrum at the bottleneck range has a positive power-lawbehavior $E(k)\propto k^\alpha$ with the power-law exponent $\alpha$approaching the value obtained in flows at thermal equilibrium $\alpha=2$. Thisagrees with the prediction of Frisch et al. [Phys. Rev. Lett. 101, 144501(2008)] who suggested that at high values of $p$, the flow should behave likethe truncated Euler equations (TEE). Nonetheless, despite the thermalization ofthe spectrum, the flow retains a finite dissipation rate up to the examinedorder, which disagrees with the predictions of the TEE system implyingsuppression of energy dissipation. We reconcile the two apparentlycontradictory results, predicting the value of $p$ for which the hyper-viscousNavier-Stokes goes over to the TEE system and we discuss why thermalizationappears at smaller values of $p$.

Turbulent cascade, bottleneck and thermalized spectrum in hyperviscous flows