Experimental Investigation of the Flow on a Simple Frigate Shape (SFS)

Abstract

Helicopters operations on board ships require special procedures introducing additional limitations known as ship helicopter operational limitations (SHOLs) which are a priority for all navies. This paper presents the main results obtained from the experimental investigation of a simple frigate shape (SFS) which is a typical case of study in experimental and computational aerodynamics. The results obtained in this investigation are used to make an assessment of the flow predicted by the SFS geometry in comparison with experimental data obtained testing a ship model (reduced scale) in the wind tunnel and on board (full scale) measurements performed on a real frigate type ship geometry.

Qualitative assessment of the bi-stable states in the wake of a finite-width double backward facing step

“…It may also be recalled that the medium mesh (M1) used here was capable of predicting both flow state I and flow state II when PANS and LES were used, respectively ). Nonetheless, the two flow states are physical and have been observed in earlier experimental studies (Herry et al (2011); Mora (2014)). The two flow states shown in Fig.…”

“…The flow topology of a frigate's flight deck is critical for flight operations; especially for quick take-off and landing of naval helicopters at various headwind conditions (see NATO (2017) guidelines). In this regard, several studies have been performed numerically and experimentally to predict the air-wake of ships and frigates (Wakefield et al (2002); Syms (2008); Forrest and Owen (2010); Herry (2010); Herry et al (2011); K€ a€ ari€ a et al (2013); Van Muijden et al (2013); Rui et al (2015); Mora (2014); Mora and Meseguer (2015); Vidales (2016); Orbay and Sezer-Uzol (2016); Gallas et al (2017); Shi et al (2017); Crozon et al (2018) and others). The flow past a frigate wake is analogous to that of a finite-width double-backward facing step (Tinney and Ukeiley (2009)), with the region behind the superstructure and the flight deck forming the top step, and the region behind the stern forming the bottom step.…”

“…2(b) shows the details of the base cavity on the top step, which extends inwards to a depth of 0:1W (' 0:23h, where h is the height of the top step) into the superstructure. The depth of the base cavity was chosen such that it did not significantly affect the volume of the superstructure/hangar, or cause an extension/protrusion that would minimise the area on the top step (heli-deck), which is critical for the safe flight operations of search and rescue helicopters (see Mora (2014) and references therein). The reduction in the drag coefficient can be observed up to a cavity depth of ' 0:3 À 0:35 times the height of an axisymmetric body in freestream (see Fig.…”

Entropy-based detached-eddy simulation of the airwake over a simple frigate shape

“…Figure 3 shows the dimensions of SFS geometry. 7 SFS model was manufactured with a hangar height of 80 mm, a beam B = 2.5H, and a flight deck length L 2 = 4.0H. The length precedent to the hangar L 1 is 8.5H, height over the floor H 1 is 0.75H, and the front height H 2 is H + H 1 .…”

“…Cheney and Zan 5,6 studied the mean surface flow topology on a 1:60 scale model of SFS using oil and pressure tappings, while the three-dimensional airwake was examined using smoke visualizations. Recently, Bardera Mora 7 further studied the flow features of SFS airwake by various experimental techniques including oil film visualization, particle image velocimetry (PIV), and laser Doppler anemometry (LDA) (Figure 1). Several wind-over-deck (WOD) conditions were investigated.…”