Experimental investigation of the flow field topology for several cargo drop configurations

Abstract

Various cargo drop configurations have been analyzed using stereoscopic Particle Image Velocimetry (SPIV). The PIV measurement planes were located at several positions in the wake of a generic transport aircraft model with an open ramp. The stream-and spanwise positioning of the wind tunnel model was facilitated by means of positioning mechanism of the wind tunnel facility. The first measured configuration consisted of only the wake of the transport aircraft. The cargo configurations consisted of a model of a cargo container, including a rigid parachute and a cargo with an airdrop support platform. A fixed haltering mechanism was used to keep the cargo at a fixed position behind the wind tunnel model for the PIV measurements. The resulting velocity fields (obtained at several chord wise positions) are used to discuss the flow topologies for these airdrop configurations. Nomenclature L, H, B = length, height and width of cargo model Re C = Reynolds number based chord length of wind tunnel model Re H = Reynolds number based on height of cargo model U ∞ = free stream velocity |V| = magnitude of velocity x, y, z = Cartesian axis system u, v, w = velocity component in x, y and z-direction, respectively α = angle of attack

Validation of the Flow Topology Around Several Airdrop Cargo Configurations at Static Conditions

“…Thus, three-component (3C) mean and instantaneous velocity field information were obtained. Details of the experimental set-up and averaged flow features were published by Roosenboom et al 16 . For the same experimental campaign a discussion of periodic and instantaneous flow features is published by the same authors 18 .…”

“…In addition, only limited amounts of seeding material were allowed by the wind tunnel operator because of unknown impact on the acoustic damping material in the recently renovated wind tunnel 19,20 . Therefore, the particle images were post-processed with background image subtraction, high-pass filtering and masking of particular regions 16,18 .…”

“…Although transient effects may have an influence on the flow 15 , the study was carried out for cargo bodies being rigidly attached to the aircraft. Experimental validation data was obtained in the low speed facility of German-Dutch wind tunnels (DNW-NWB) in Braunschweig, Germany, in 2011 by means of stereoscopic Particle Image Velocimetry (SPIV) 16 . This data basically contains information on the mean and instantaneous velocity field in the near-field of the aircraft and around the cargo bodies.…”

Development and Validation of a RANS-based Airdrop Simulation Approach

“…In contrast to the conclusions of the aforementioned research groups DLR has decided to stick with its Reynolds-averaged Navier-Stokes flow solver TAU to examine and predict the airdrop trajectories. Based on a vast experimental data base, including PIV flow field 15,16 and trajectory measurements, 17 the suitability of the DLR TAU code to predict the general flow field 18,19 as well as first trajectories 20 was successfully demonstrated. Based on these promising results DLR further matured its high-fidelity approach and currently is able to predict the motion of simplified 6-DOF, 7-DOF and 8-DOF cargo and cargo-parachute systems within the vortical wake of the aircraft.…”