Ship Air Wake Wind Tunnel Test Results (Invited)

Abstract

As part of a larger program to develop analytic and computational tools to predict the air wake characteristics of naval vessels, an experimental effort has been undertaken to map the air wake of a scaled patrol craft modified with a representative hangar structure and stern flight deck. A 4% scaled model of a United States Naval Academy YP (Patrol Craft, Training) was fabricated for wind tunnel testing at 0, 15, and 30 degrees of yaw at a Reynolds number of 7.6 million. The topside configuration of the vessel simulates that of larger destroyers and cruisers, which service rotorcraft from stern hangars and flight decks. Flow measurements were made in station planes from 0.45 to 5.14 hangar-heights downstream of the aft hangar face using an 18-hole Omniprobe. The 3D velocity measurements indicated that a recirculation zone occurred over the flight deck and extended from 1.5-3 hangar-heights downstream. The effect of yaw angle on the air wake was to consolidate and shift the rotationality of the flow into a large, leeward vortex with a size on the order of the superstructure height. Furthermore, the unsteadiness of the flow was independent of the survey plane position at zero yaw, but increased by 57% at 30 deg yaw, with a large band of high vorticity where the shear layer separated and rolled up. The velocity distributions, flow angles, and vorticity will be used to compare with computational fluid dynamics (CFD) and full-scale, in-situ measurements to portray a complete, Reynoldsscaled picture of the air wake. NomenclatureCCWT = closed-circuit wind tunnel CFD = computational fluid dynamics CG = guided missile cruiser CVN = multi-purpose aircraft carrier (nuclear) DDG = guided missile destroyer ESP = electronically-scanned pressure H = hangar reference height  = model reference length LHA = amphibious assault ship (general purpose) p = fluid pressure q = dynamic pressure, ( ) 2 2 V ρ T = fluid temperature U = Measurement uncertainty estimate V  = velocity vector V = velocity magnitude u = x-component of velocity v = y-component of velocity w = z-component of velocity x = distance aft of the hangar face y = distance starboard of the vessel centerline z = distance above the flight deck surface 2 WISP = wake interactive survey probe YP = Naval class designation for "patrol craft, training" Greek α = flow pitch angle β = flow yaw angle δ = probe bias error ∆ = differential ε = test section blockage correction factor ζ  = vorticity, V ∇ ×  ρ = fluid density ω  = angular velocity, 2 ζ  Subscripts corr = measurement corrected for bias error p ∆ = pertaining to probe pressure differential probe = measurement referenced to probe position and mount orientation T = stagnation (total) condition V = pertaining to velocity SB = solid blockage WB = wake blockage ∞ = freestream condition

Validation of Computational Ship Air Wakes for a Naval Research Vessel

“…In prior updates to this project, [13][14][15][16][17][18][19][20][21][22][23][24] we noted the following results:…”

Insight into the factors affecting the safety of take-off and landing of the ship-borne helicopter

“…In a headwind, the longitudinal axis of the recirculation zone is roughly two to three times the hangar height, and the lateral axis is the width of the hangar. 39,40 The increase in the hangar height and/or relative wind speed usually results in an increase in the strength of the recirculation zone. And the relative wind angle will also influence the location, strength, size, and shape of the recirculation zone.…”

Wireless telemetry system for real-time estimation of ship air wakes with UAVs

“…The computer-aided designs of the model and environment are often simplified to reduce computation loads making computational methods insufficiently validated for systems with complex structures. In addition, these simulations often need experimental validation using anemometer sensors, which have their respective drawbacks [5][6][7][8][9].…”