Dr. Aaron Johnson is a mechanical engineer with expertise in fluid dynamics and flow measurement. His interests include measuring flue gas flows, measuring pipeline-scale natural gas flows, designing primary flow standards, analyzing the uncertainty of flow measurements, computational fluid dynamics, and modeling flow meters (e.g., critical flow venture meters, turbine meters, ultrasonic meters).
Dr. Johnson has leadership roles in three projects:
- developing a scale-model smokestack simulator. The simulator's diameter (1.2 m) is approximately 1/10th the diameter of the stack of a typical, coal-fired power plant. The simulator will (a) quantify the accuracy of flow meters used in smokestacks, (b) quantify uncertainties of stack-flow measurement protocols, and (c) test alternative, low-uncertainty flow-measurement technologies (e.g., long-wavelength acoustic meters, multipath ultrasonic techniques). By facilitating accurate stack flow measurements with quantified uncertainties, the simulator supports programs that place a price on the emissions of coal-burning power plants.
- developing and maintaining NIST's internationally-recognized, natural gas flow calibration service that provides industry low-uncertainty (0.22 % to 0.4 %) flow measurements. These measurements are traceable to primary flow standards developed and maintained by NIST. Flow meters serve as "cash registers" during custody transfers of natural gas; they determining the money exchanged between buyers and sellers. NIST's natural gas calibration service facilitates equitable custody transfer within the U.S. and in international commerce.
- improving gas flow meter calibrations performed under non-ideal flow conditions including (a) swirling, asymmetric flows typical of smokestacks, and (b) transient and quasi-stable flows typical of blow-down methods. Blow-down methods are used to calibrate meters with flows that are too large (> 10 kg/s) to maintain in a steady state laboratories. To facilitate calibrations under these non-ideal circumstances, Johnson is "taking the lab to the field;" thereby making NIST's calibrations more useful to its customers.