Low-density multi-fan wind tunnel design and testing for the Ingenuity Mars Helicopter

Prior to its successful flights on Mars, the Ingenuity Mars Helicopter system underwent extensive flight dynamics testing in the 25-ft Space Simulator facility, a low pressure environmental chamber at NASA’s Jet Propulsion Laboratory (JPL), which can re-create relevant Martian conditions on Earth. This facility, while large, is not large enough for free or tethered forward flight tests. In this work, an open-jet, multi-fan wind tunnel concept is presented, which was integrated into the JPL facility to simulate the external freestream flow of forward flight scenarios in a low-density environment. A theoretical and experimental analysis was performed to evaluate the possibility of utilizing commercially available 80 x 80 mm axial flow cooling fan units for this type of wind tunnel. Sub-scale tests found that under Martian conditions, fans deliver approximately 30% reduced flow rates for the same RPM compared to Earth conditions due to decreased efficiencies at low Reynolds numbers. However, fans can run at higher RPM in low-density fluids, with the RPM increase being specific to the fan motor. While power consumption dropped by more than 90%, fans experienced higher thermal loads due to reduced heat convection. The study concludes that the investigated type of cooling fan can operate without modification in a low-density environment, offering a low-cost and easily adaptable wind tunnel solution. Informed by ambient flow field measurements on a comparable multi-fan wind tunnel, a low-density full-scale facility with 441 individually controlled fan units was constructed and used for aerodynamic testing of an engineering model of Ingenuity.