EXPERIMENTAL AND COMPUTATIONAL STUDIES OF THE FLOW CHARACTERISTICS OVER A GENERIC AIRCRAFT CARRIER WITH AND WITHOUT THE ISLAND.
Creators: name: Kumar, K Vignesh
Publisher: name: figshare
Year: 2021
Subjects: subject: 91501 Computational Fluid Dynamics
subject: FOS: Other engineering and technologies
subject: 91102 Naval Architecture
subject: FOS: Environmental engineering

description: Naval aviation is a fascinating and complex field of military operations. Compared to land-based aviation facilities, aircraft operating from ships at sea are burdened with constraints of space and challenging environmental conditions. The epitome of ship borne flight operations is the operation of fighter aircraft from an aircraft carrier, which is a large ship that serves as a full-fledged floating air base, capable of launching and recovering aircraft from its flight deck. Landing an aircraft on a carrier ranks as one of the most demanding tasks for naval pilots. The limited length of landing runway available, seakeeping motions of the landing platform, high landing speeds required for fighter aircraft etc., make the landing operation a complex evolution. Additionally, the superstructure (island), deck/hull edges and other physical features of the carrier, generate turbulent air wake characterized by regions of large separated flows. In aviation parlance, this zone of disturbed flow is called the 'burble' and is encountered by pilots during their landing approach. These factors impose high workload on the pilot during the critical landing phase and lead to pilot errors, touch-and-go landing attempts (‘bolters’) and cause flight accidents. The motivation for the present study is to ease pilot workload and thereby reduce carrier landing accidents, by studying and improving flow in the carrier environment. The study focusses on the effect of the island, on the flow in the flight approach zone and investigates sensitivity of the burble to island location. iv Due to the classified nature of military data, very less information is available in open domain regarding flow studies on aircraft carriers. Recognizing that there is presently no common benchmark model for aircraft carriers (akin to the internationally accepted Simple Frigate Shape-SFS), a simplified Generic Aircraft Carrier (GAC) model that inherits the salient aerodynamic traits of all actual aircraft carriers in service, is developed as part of the present study. A comprehensive database of experimental data is generated by testing the GAC model in the IIT Delhi Wind Tunnel. Pressure distribution over the deck of the GAC is measured using 105 pressure taps installed at discrete locations covering the entire flight deck. A novel design concept of raising the island clear off the deck, supported on cylindrical pillars, is proposed as a feasible solution to improve flow in the flight approach zone. Pressure distribution is measured over three variants of GAC (without island, with island and raised island) for comparison of the effect of the island in modifying the flow in each case. In the second phase of experiments, Particle Image Velocimetry is employed to measure velocity and turbulence intensity in the carrier environment, which are identified as the principal contributors to pilot workload from literature. Smoke visualization and tufts are used to undertake extensive flow visualization experiments to obtain corroboratory insights into the flow features. The experimental domain is modelled numerically in CFD using ANSYS FLUENT and a thorough validation study is undertaken to identify an adequate turbulence model that predicts the flow in the carrier environment with acceptable v accuracy. The validated numerical model (SST k-w) is engaged to parametrically vary the island location and study the effect on flow in the flight approach zone. Numerical indices relating to pilot workload are specifically formulated in the present study, to qualify the relative merit of different configurations based on statistics of flow parameters measured along flight approach path. Preliminary design guidelines for favourable island position are derived from the parametric investigation, to aid future aircraft carrier concept designs. Scope for future work in the field, is also suggested, to build upon the foundation laid by the present study.