We explore the formation of superbubbles through energy deposition by multiple supernovae ( SNe ) in a uniform medium .
We use total energy conserving , 3-D hydrodynamic simulations to study how SNe correlated in space and time create superbubbles .
While isolated SNe fizzle out completely by \sim 1 Myr due to radiative losses , for a realistic cluster size it is likely that subsequent SNe go off within the hot/dilute bubble and sustain the shock till the cluster lifetime .
For realistic cluster sizes , we find that the bubble remains overpressured only if , for a given n _ { g 0 } , N _ { OB } is sufficiently large .
While most of the input energy is still lost radiatively , superbubbles can retain up to \sim 5 - 10 \% of the input energy in form of kinetic+thermal energy till 10 Myr for ISM density n _ { g 0 } \approx 1 cm ^ { -3 } .
We find that the mechanical efficiency decreases for higher densities ( \eta _ { mech } \propto n _ { g 0 } ^ { -2 / 3 } ) .
We compare the radii and velocities of simulated supershells with observations and the classical adiabatic model .
Our simulations show that the superbubbles retain only \lesssim 10 \% of the injected energy , thereby explaining the observed smaller size and slower expansion of supershells .
We also confirm that a sufficiently large ( \gtrsim 10 ^ { 4 } ) number of SNe is required to go off in order to create a steady wind with a stable termination shock within the superbubble .
We show that the mechanical efficiency increases with increasing resolution , and that explicit diffusion is required to obtain converged results .