A Hybrid Methodology to Evaluate the Effects of Trip Disks on Transonic Wind Tunnel Models

A study was conducted to enhance the analytical modeling of the laminar-to-turbulent transition initiated by trip disks placed on a wind tunnel model at transonic speeds. Trip disks are the standard technique used in the Boeing Transonic Wind Tunnel for tripping the laminar boundary layer. The study consisted of wind tunnel testing and CFD analyses aimed at predicting the drag increment resulting from the trip disks. The experiments were conducted in the low speed wind tunnel at the Institute of Theoretical and Applied Mechanics in Novosibirsk, Russia. In the experiments, the laminar boundary layer profiles were measured at the trip location and turbulent profiles were measured at a series of downstream locations. These profiles were used to develop a trip model, describing the change in profile characteristics behind the row of trip disks. The trip model describes the turbulent boundary layer as a function of the laminar profile characteristics and the trip height. This trip model was then used in the CFD code TRANAIR to determine the trip drag increments on a transonic airplane model. The standard integral boundary layer model in TRANAIR was modified to enable the imposition of a step change in trip conditions generated using the trip model. Transonic wind tunnel data was used to calibrate the TRANAIR transition modeling. The CFD code was used to analyze a wide range of flow conditions, where wind tunnel data was also available. The overall agreement between the wind tunnel results and the CFD is shown to be excellent.