Simulation and analysis of puffing instability in the near field of pure thermal planar plumes

► Correlation between puffing instability and lapping flow instability was found. ► Effect of lapping flow velocity on bulge forming was studied with channel flow model. ► A mapping of bulge formation against Reynolds and Froude numbers was obtained. ► Bulge was found to form further downstream with increasing Froude number. ► Oscillation frequency was found to scale with Reynolds and Froude numbers.