  Open clusters are key tools to study the spatial distribution of abundances
in the disk and their evolution with time. Using the first release of stellar
parameters and abundances of the Gaia-ESO Survey, we analyse the chemical
properties of stars in three old/intermediate-age open clusters, namely NGC
6705, NGC 4815, and Trumpler 20, all located in the inner part of the Galactic
disk at Galactocentric radius R$_{GC}\sim$7 kpc, aiming at proving their
homogeneity and at comparing them with the field population. We study the
abundance ratios of elements belonging to two different nucleosynthetic
channels: $\alpha$-elements and iron-peak elements. The main results can be
summarised as follows: i) cluster members are chemically homogeneous within
3-$\sigma$ in all analysed elements; ii) the three clusters have comparable
[El/Fe] patters within $\sim$1-$\sigma$, but they differ in their global metal
content [El/H], with NGC 4815 having the lowest metallicity. Their [El/Fe]
ratios show differences and analogies with those of the field population, both
in the solar neighbourhood and in the bulge/inner disk; iii) comparing the
abundance ratios with the results of two chemical evolution models and with
field star abundance distributions, we find that the abundance ratios of Mg,
Ni, Ca in NGC 6705 might require an inner birthplace, implying a subsequent
variation of its R$_{GC}$ during its lifetime, consistent with previous orbit
determination. The full dataset of the Gaia-ESO Survey will be a superlative
tool to constrain the chemical evolution of our Galaxy by disentangling
different formation and evolution scenarios.
