Ship Airwake Sensitivities to Modeling Parameters

Abstract

** * † Accurate models for the prediction of ship airwake flowfields are critical to the development of realistic flight simulation tools for aircraft carrier launch and recovery operations. The accurate computation of the ship airwake can be very challenging due to the complexity of the ship geometry, the size of and difficulty in generating a suitable computational mesh, and the large range of length and time scales present in the unsteady flowfield. The present paper investigates the sensitivity of the airwake solution to several modeling parameters, including geometric complexity and the resolution of boundary layers, with the aim of determining the level of fidelity required to obtain an accurate solution. Results are compared to wind tunnel experimental measurements. The results of these studies show that, in general, a majority of the airwake flow features are characterized by bluff body shedding from the larger geometric entities that comprise the ship geometry. Depending on the requirements and intended use of the solution, a certain tradeoff can be reached between solution turn-around/grid generation time and solution accuracy. I. Introduction HE integration of aircraft with air capable ships is both a challenging and expensive task that carries an inherent risk to pilots. New V/STOL aircraft and rotorcraft in particular, such as the Joint Strike Fighter (JSF) and V-22, encounter unique challenges in performing takeoff and landing maneuvers during the course of shipboard operations due to the interaction of the propulsion-generated downwash with the unsteady airwake generated by the ship superstructure & deck. For such aircraft, wind-over-deck (WOD) launch and recovery envelopes must be developed, relating the compatibility of the specific aircraft with a specific ship at specific flight/wind conditions. This is currently accomplished through expensive, time-consuming sea trials for every aircraft and ship combination. Such trials entail numerous landing and takeoff operations, while incrementally (e.g., 5 knots speed or 15 degrees azimuth change) varying the WOD conditions. For multiple landing spot platforms, flight envelopes must be developed for each spot. The limits of the flight envelope are determined from the test pilot’s subjective rating of the landing/take-off, taking into account factors such as pilot workload, flight control and power limitations of the aircraft, and ship motion. Safety is an additional issue of significant concern during these trials, due to the unknown response of the aircraft to the wind conditions. Modeling and simulation of the dynamic interface between the ship airwake environment and the aircraft can potentially reduce the cost and risk associated with these tests by providing a process for determining WOD performance envelopes via piloted flight simulation. 1,2,3 A crucial aspect involves the incorporation of physical models of the various subsystems into the flight simulator environment, including computational fluid dynamics (CFD) models of the ship airwake and aircraft propulsive flowfields. T