Upside-down jellyfish, Cassiopea spp., are prevalent in warm and shallow parts of the oceans throughout the world. They are unique among jellyfish in that they rest upside down against the substrate and extend their oral arms upwards. This configuration allows them to continually pull water along the substrate, through their oral arms, and up into the water column for feeding, nutrient and gas exchange, and waste removal. Although the hydrodynamics of the pulsation of jellyfish bells has been studied in many contexts, it is not clear how the presence of oral arms alters the jet formed by these jellyfish. Furthermore, it is not clear how the muscular activation and elastic properties of the bell generate bell motion that results in a sustained upward jet. In this paper, we use three-dimensional 3D immersed boundary simulations to characterize the flow generated by upside-down jellyfish with and without oral arms. Experimental results are used to validate numerical simulations with and without the oral arms. Preliminary results show that the presence of the oral arms creates a flow pattern where new water is brought to the medusa from along the substrate during each pulse cycle. This volume of water is then ejected upwards during the contraction phase. We will also present results that show how the pulse frequency, muscle activation strength, and bell elastic properties are tuned to generate a strong upward jet.