STUDY OF THE SHIP AIRWAKE AND HELICOPTER DOWNWASH CHARACTERISTICS FOR SAFE HELO OPERATIONS
Creators: name: Shrish Shukla
Publisher: name: figshare
Year: 2021
Subjects: subject: Aerospace Engineering
subject: FOS: Mechanical engineering
subject: FOS: Mechanical engineering

description: The operation of helicopters at ships on-board has always been a very complex task owing to the presence of ship air wakes, high-velocity gradients, widely varying turbulence length scales as well as the bluff shape ship superstructures. Further, this complexity increases with the addition of helicopter downwash during landing/take off. In addition, these difficulties are more critical for small category frigate class ships. This is mainly due to (i) compactness in shape and size along with fixed design considerations, (ii) the sea-keeping motions encountered in high seas provide a non-stationary oscillating platform, and (iii) the visual cues reduce drastically due to sea spray. Further, the onboard landing deck area is limited (typically twenty percent the entire ship top deck area) due to the vessel stability constraint. In essence, the above-mentioned constraints lead to shipborne helicopter operation being one of the most challenging and difficult tasks in every naval organisation. Hence, an early assessment of the resultant flow environment over the ship helodeck for at early design stage is very crucial to minimise the risk associated with the shipborne helicopter operation. The study is thus aimed to seek a suitable cost-effective early-stage preliminary design tool to evaluate the essential flow features of coupled ship-helo airwake and overcome the complexities associated with shipborne helicopter operations. The study utilises the available experimental and numerical resources to understand the combined ship-helo airwakes characteristics on helodeck contributing to influence the helicopter aerodynamics, and explore solutions for economical early-stage approach in order to improve the safe ship-helo operations margin. The ship airwakes and their effect over the flow characteristics of the flight deck region have been analyzed experimentally and computationally. An outstanding problem is to operate a helicopter in the regions of coherent, high-amplitude/less-frequency turbulence flow, which develop from the sharp edges and additional bluff bodies on the ship superstructure. Therefore, in order to gain insight into the ship airwake characteristics, the experiments have been undertaken on internationally accepted Simplified Frigate Ship (SFS2) along with the helicopter fuselage (ROBIN) at the initial stage of investigations. The experimental investigations have been undertaken into two stages. In the first stage, the isolated ship airwake case has been studied experimentally. The combined ship-helo configurations have been extensively investigated with respect to the flight approach path followed on onboard helicopter operations over the helodeck in the second stage of experimental study. Subsequently, the steady flow investigations have been undertaken in order to establish a suitable numerical methodology to reasonably capture the flow characteristics of the experimental studies in the third stage of the study.