I would say, it depends on the requirement (domain and applications). I prefer ANSYS, StarCCM+, and COMSOL. Moreover, all of these are effective but vary based on your level of expertise.
Hello Sahitya Yadav. I would recommend Ansys CFX and COMSOL for simulating unsteady multiphase flow. Because they are user-friendly. I have used ANSYS CFX for simulating Gas-Liquid Multiphase flow in Radial Blade pumps as well as in Electrical Submersible pumps. You can learn from the following articles. Hope it will be helpful for you. Best regards,
Article Research Progress and Prospects of Multi-Stage Centrifugal P...
Article Experimental and Numerical Study on Gas-Liquid Two-Phase Flo...