Computational fluid dynamics simulations of ship airwake N Sezer-Uzol, A Sharma, and L N Long à Department of Aerospace Engineering, Pennsylvania State University, Pennsylvania, USA The manuscript was received on 17 March 2005 and was accepted after revision for publication on 26 August 2005. DOI: 10.1243/095441005X30306 Abstract: Computational fluid dynamics (CFD) simulations of ship airwakes are discussed in this article. CFD is used to simulate the airwakes of landing helicopter assault (LHA) and landing platform dock-17 (LPD-17) classes of ships. The focus is on capturing the massively separated flow from sharp edges of blunt bodies, while ignoring the viscous effects. A parallel, finite- volume flow solver is used with unstructured grids on full-scale ship models for the CFD calcu- lations. Both steady-state and time-accurate results are presented for a wind speed of 15.43 m/s (30 knot) and for six different wind-over-deck angles. The article also reviews other compu- tational and experimental ship airwake research. Keywords: ship airwake, computational fluid dynamics, landing helicopter assault (LHA), landing platform dock-17 (LPD-17), dynamic interface, blade sailing 1 INTRODUCTION Helicopter shipboard operations present a multitude of challenges. One of the primary factors that make it extremely difficult, and potentially dangerous, to perform helicopter flights to and from a ship deck is the unsteady ship airwake. Other factors that are also important are the possibly adverse weather and sea conditions, ship translation and rotation (oscillating landing spot), small flight decks (for some ships), and poor visibility conditions. The most challenging rotorcraft/ship dynamic interface (DI) problems occur during: (a) engagement and disengagement (run-up and run-down) of the rotor system while the aircraft is on the flight deck (i.e. the blade-sailing phenomena); (b) takeoff and landing operations (e.g. launch, departure, approach and recovery); (c) hovering over the moving flight deck (i.e. station-keeping). It requires tremendous practice and skill for the pilots to learn to perform these operations. A common practice to ensure safe operation of helicopters from a ship is to find the safe helicopter operating limits (SHOLs) for a ship/helicopter combination. These are usually defined in terms of allowable wind conditions (direction and speed) over the deck and are called wind-over-the deck (WOD) envelopes. It is difficult to obtain these WOD envelopes using real, full-scale experiments for a variety of reasons. A series of DI flight tests for all possible combi- nations of wind speed and azimuth (typically in 5 knot, 158 increments) must be performed to estab- lish the envelope. However, these tests are costly, often limited (due to the absence of certain wind conditions and the availability of fleet assets), and unsafe. This process also depends on subjective pilot ratings. In contrast, scale model wind tunnel tests allow control over the wind conditions and can supply detailed information but are still costly and time consuming. In wind tunnel testing, small size ships (with lower Reynolds number) are used and the full-scale (high) Reynolds number cannot be obtained. In addition, the complexity of the flow field of a rotorcraft during takeoff and landing is impossible to reproduce in a wind tunnel. Fur- thermore, it is both difficult and costly to obtain high quality and complete sets of coupled ship air- wake/rotorcraft flow field measurements using both full-scale and scaled-model tests for all of the different WOD conditions for any ship/helicopter à Corresponding author: Department of Aerospace Engineering, Pennsylvania State University, University Park, PA 16802, USA. SPECIAL ISSUE PAPER 369 G01105 # IMechE 2005 Proc. IMechE Vol. 219 Part G: J. Aerospace Engineering at IOWA STATE UNIV on February 27, 2015 pig.sagepub.com Downloaded from