Increasing use of helicopters in conjunction with ships poses many major problems. In the presence of high winds and rough sea, excessive ship motions and turbulent separated flow from Sharp-edged box-like ship super-structures make landing a helicopter on ships a very hazardous operation. The strong unsteady flows can cause severe rotor blade deformations. There have been numerous incidences where the helicopter blades have actually impacted the helicopter fuselage, which is called a 'tunnel strike'. Statistically, a helicopter can safely land on a frigate in the North Sea only 10 percent of the time in winter. In addition, flight simulators also have no adequate models for airwake. In order to avoid this and other engage/disengage problems, determining safe operating envelopes is very costly and time consuming. On the other hand, many numerical simulation attempts of this flow field for minimizing cost have not been successful due to the inherently unsteady nature of flow and the low-speed character of the flow (which may cause numerical stiffness).
Recent research on ship airwakes has been conducted from several different approaches[5]. One of the sources of relevant research is building aerodynamics which shows the general features of flow about blunt bodies of different aspect ratios, and about clusters of buildings. The most likely model of a ship, but rather crude, is a sharp edged blunt body. More geometrically precise studies have been done in wind tunnel tests [8] [6] [7] and full scale tests of the US Navy [11], which gives some important information on real ship airwakes. All these experimental tests are crucial for validating numerical models. Wind tunnel tests can be quite costly, but the flow measurements on real Naval ships is very difficult and costly to obtain.
It would be very useful to have numerical methods that could simulate ship airwakes. There have been other attempts at numerically simulating ship airwakes, e.g. a steady-state flow solver based on the 3D multi-zone, thin-layer Navier-Stokes method [13] and an unsteady inviscid solver low-order method [12]. No method to-date has been entirely satisfactory for predicting these flow fields.