A viscosity solution approach to the large deviation principle for stochastic convective Brinkman-Forchheimer equations

This article develops the viscosity solution approach to the large deviation principle for the following two- and three-dimensional stochastic convective Brinkman-Forchheimer equations on the torus ${\mathbb{T}}^d,d\in \{2,3\}$ with small noise intensity: \begin{align*} $\mathrm{d}$\boldsymbol{u}_n+[-μΔ\boldsymbol{u}_n+ (\boldsymbol{u}_n\cdot\nabla)\boldsymbol{u}_n +α\boldsymbol{u}_n+β|\boldsymbol{u}_n|^{r-1}\boldsymbol{u}_n+\nabla p_n]$\mathrm{d}$ t=\boldsymbol{f}$\mathrm{d}$ t+\frac{1}{\sqrt{n}}$\mathrm{Q}$^{\frac12}$\mathrm{d}$$\mathrm{W}$, \ \nabla\cdot\boldsymbol{u}_n=0, \end{align*} where $\mu ,\alpha ,\beta >0$, $r\in [1,\mathrm{\infty })$, $\mathrm{Q}$ is a trace class operator and $\mathrm{W}$ is Hilbert-valued calendrical Wiener process. We build our analysis on the framework of Varadhan and Bryc, together with the techniques of [J. Feng et.al., Large Deviations for Stochastic Processes, American Mathematical Society (2006) vol. $\mathbf{\text{131}}$]. By employing the techniques from the comparison principle, we identify the Laplace limit as the convergence of the viscosity solution of the associated second-order singularly perturbed Hamilton-Jacobi-Bellman equation. A key advantage of this method is that it establishes a Laplace principle without relying on additional sufficient conditions such as Bryc’s theorem, which the literature commonly requires. For $r>3$ and $r=3$ with $2\beta \mu \ge 1$, we also derive the exponential moment bounds without imposing the classical orthogonality condition $(({\mathit{u}}_n\cdot \mathrm{\nabla }){\mathit{u}}_n,\mathrm{A}{\mathit{u}}_n)=0$, where $\mathrm{A}=-\mathrm{\Delta }$, in both two-and three-dimensions. We first establish the large deviation principle in the Skorohod space. Then, by using the $\mathrm{C}-$exponential tightness, we finally establish the large deviation principle in the continuous space.