A method for producing a three-dimensional object by selectively solidifying a build material applied layer by layer includes, in at least one process chamber, applying the build material layer by layer to a build platform, generating at least one beam for solidifying the build material using a radiation source, feeding the at least one beam to the build material in the build platform using at least one beam guiding element, and generating a primary gas flow along the build platform using a process assistance device. The process assistance device includes a centre module and at least one outer module aligned with the centre module, so that a section over which primary gas flows is formed between the centre module and the at least one outer module. The centre module and/or the at least one outer module are triggered so as to be movable along the build platform.