Task farming is often used to enable parameter sweep for exploration of large sets of initial conditions for large scale complex simulations. Available solutions enable to perform parameter sweep by creating multiple grid job submissions with different parameters. This paper presents an approach to farm grid workflows with a web service based workflow management system, called WS-VLAM, which provides ways to create, control and monitor workflows applications and their components. An approach to balance the workload between the workflow instances and to collect provenance data at both system and workflow levels is also discussed. Finally, an experimental evaluation of the presented solution is performed with a biomedical application for which 3000 simulations were required to perform a Monte-Carlo study.