High energy observations show the presence of cosmic rays (CRs) in OB associations, and it is also theoretically expected, since massive stars are usually born in such associations. We have studied various aspects of CRs acceleration in these star clusters, using analytic methods and $1$-D/$3$-D two-fluid cosmic ray (CR) hydrodynamic simulations. We investigated two different CR injection scenarios, namely, (a) injection in the central wind-driving region and (b) injection at the resolved shocks. We find that, in model (a), the thermal profile gets significantly affected by CRs when (i) the Mach number of the shock exceeds $M_{\rm th}\gtrsim 12$ and (ii) the dynamical time is longer than the CR acceleration time scale $\tau_{\rm acc}\sim \kappa_{\rm cr}/v^2$ ($\kappa_{\rm cr}$ is the CR diffusion coefficient and $v$ is the upstream velocity). In order to compare with observations, we estimate the gamma-ray, X-ray and radio luminosities, which allow us to identify the reverse shock as a main CR acceleration site in the interstellar bubbles. We show how multi-wavelength observation can constrain the CR injection parameters.

(Reference: 1. Gupta, S., Nath, B. B., Sharma, P. and Eichler, D. 2018 MNRAS, 473, 1537, 2. Gupta et al in preparation)