Trans RINA, Vol 152, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun


SUPER YACHT AIRWAKE: COMPARING METHODS OF ASSESSMENT AND THEIR APPLICATION TO DESIGN


G S Hawkes, R M Scott, C J Carter and A Payne, Frazer-Nash Consultancy Limited, UK (DOI No: 10.3940/rina.ijsct.2010.b1.94)


SUMMARY


Understanding the aerodynamic environment, or airwake, around a super yacht is a key area of consideration to the naval architect during design. The airwake is characterised by structure-induced flow disturbances and the presence of ventilation and exhaust plumes.


dispersion of gases away from the yacht, and passenger and crew comfort. If the airwake is poorly understood, contractual requirements may not be met and certification may not be achieved. characterised by wind tunnel tests of scale models.


These features may significantly influence the safety of helicopter operations, the Traditionally, airwake has been


Although mature and well understood, a number of significant


challenges remain to the ease with which airwake assessments can be included during yacht design and risk reduction activities during the bid stage. Broadly speaking, the key experimental challenges are the requirements for a detailed scale model, means of data capture and storage, and consistent scaling of flow and thermal effects. An alternative approach is to predict the airwake using Computational Fluid Dynamics modelling. This paper discusses the application of airwake assessments to super yacht design and reviews both experimental and computational approaches in terms of the associated costs and benefits to the designer. The results of a computational airwake assessment for a typical large yacht are presented in terms of quantifying the turbulence field and thermal disturbances within the wake of the superstructure.


Finally, recent developments in turbulence simulation are discussed with reference to their future potential uses in airwake modelling.


NOMENCLATURE C


g k


L


U* v’


u’ U


w’ z


z0 Re Charnock number


Gravitational acceleration (ms-2) Turbulent kinetic energy (m2s-2) Characteristic length scale (m) Velocity fluctuation in x-axis (ms-1) Free stream velocity (ms-1) Mean wind speed (ms-1)


Velocity fluctuation in y-axis (ms-1) Velocity fluctuation in z-axis (ms-1) Elevation above sea surface (m) Equivalent roughness (m) Reynolds number


σ Gust velocity (ms-1) ν Kinematic viscosity (m2s-1) ω Specific dissipation rate (s-1)


1. INTRODUCTION


Understanding the aerodynamic environment, or airwake, around a super yacht (Figure 1) is a key area of consideration to the naval architect during design. The airwake is characterised


by structure-induced flow


disturbances and the presence of ventilation and exhaust plumes.


is poorly understood, contractual


safety of helicopter operations, the dispersion of gases away from the yacht, and passenger and crew comfort. the airwake


These features may significantly influence the If


requirements may not be met and certification may not be achieved.


This paper discusses the relative merits and costs of experimental and computational approaches to airwake assessment to support certification. The results of a fully


©2010: The Royal Institution of Naval Architects


Figure 1: The complex superstructure and mast fitment of a typical modern super yacht.


2. NEED FOR AIRWAKE ASSESSMENT 2.1


CERTIFICATION AND ACCEPTANCE


In today’s times super yachts are seen as both a luxury and a significant investment. In order for a vessel to be accepted as suitable for commercial charter it must be demonstrated to adhere to an appropriate design code and accepted by the corresponding agency, for example the Maritime and Coastguard Agency (MCA). Whilst there are many elements of certification which relate to all aspects of design and operation, one specific element which forms the subject of this paper is the requirement to enable safe rotorcraft operation. Certification of the


computationally based assessment are presented to demonstrate the capabilities of modern predictive techniques.


Finally, recent advances in turbulence


simulation are discussed with reference to their future application for airwake assessment.


B-21


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