Helicopter ground vortex: comparison of numerical predictions with wind tunnel measurements

Abstract

In the framework of the Brite Euram project HELIFLOW, research activities were conducted aimed at knowledge acquisition in the area of interactional aerodynamics, validation of wind tunnel test technologies and verification of related theoretical tools. This paper describes the ground vortex activities performed in Task 3 of the project, which addressed the low speed phenomena of quartering flight. During sideward flight in ground proximity, the helicopter main rotor induced ground vortex influences the main and tail rotor inflow conditions and thus its performance. Wind tunnel tests were performed with a powered BO 105 model in the Large Lowspeed Facility (LLF)of the German-Dutch Wind Tunnels (DNW). State of the art airflow test techniques were applied to measure the ground vortex flow phenomena. The in-house developed OUTWASH code was extended with several features for application within HELIFLOW. It was applied for pre-test calculations to refine the wind tunnel test matrix and to define the experimental set-up for the flow measurements by calculating the ground vortex locations. Based on the test results obtained, an OUTWASH analysis activity was performed. Specific attention was given to the numerical and experimental assessment of the ground vortex core position and velocity distribution.