[Tex/LaTex] add vertical space between equations

Question

I am using the following code to combine two equations with one number in parentheses but the two equations are very close to each other and using '\vspace{} not working

How can i add a vertical space between these two equations ?

\begin{equation}
 \begin{aligned}
T_{P} = K_{T}. \rho . n^{2}_{p} . D^{4}_{p} \\ 
Q_{P} = K_{Q}. \rho . n^{2}_{p} . D^{5}_{p}
\end{aligned}
\end{equation}

Answer 1

You can manually add a vertical distance to each line-break. I hope, this is what you want.

% arara: pdflatex

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\setcounter{equation}{2}
\begin{equation}
    \begin{aligned}
        T_{P} &= K_{T}. \rho . n^{2}_{p} . D^{4}_{p} \\[1pt]
        Q_{P} &= K_{Q}. \rho . n^{2}_{p} . D^{5}_{p} \\[10pt]
        N_{P} &= K_{N}. \rho . n^{2}_{p} . D^{6}_{p} \\[100pt]
        K_{P} &= K_{K}. \rho . n^{2}_{p} . D^{7}_{p}
    \end{aligned}
\end{equation}
\end{document}