Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019


workload, the second criteria will be the Downdraft Criteria wherein the vertical component of velocities over the rotor plane should be reduced. The word downdraft here comprises of both upward and downward vertical velocity component and both are considered undesirable.


c) One of the conclusions of the literature survey indicated that a higher relative wind velocity is a favourable condition for a helo pilot because it increases the power and torque limits that are available to him for control of helo. Accordingly, the third candidate for the criteria set should ensure that the Relative Wind Velocity in the direction of fore and aft line of helicopter (akin to head wind for helo while operating ashore) for a given hangar configuration over the rotor plane should be increased for an improved environment for helo handling.


d) The length of recirculation, as a flow parameter on helodeck, has been extensively investigated in literature. Though the design and length of contemporary helodeck may ensure that the helo operations are undertaken outside the extent of recirculation zone, it can be expected that a reduction in the extent of recirculation zone (even when located outside the actual helo operating radius) will indirectly lead to an increase in the relative velocity on rotor planes by reducing the low momentum area behind the hangar. Also, a reduction in the length of recirculation is expected to increase the distance between the shear layer and the helo landing area which in turn should lead to reduction in turbulence on the rotor planes. Accordingly, the length of the recirculation zone should be minimised for an improved ship-borne helo operation.


e) The presence of the superstructure in front of the operating helo makes the relative velocity incident on to the rotor uneven. Such an unevenness will result in a resultant moment on the helo due to the uneven lift forces created by the rotor. Accordingly, the value of standard deviation of the relative velocity on the rotor plane, which represents the non-uniformity of the relative velocity incident onto the rotor, should tend to zero for a better incident flow environment for the helo.


An analysis with the above proposed criteria set can be used to undertake a comparative analysis between competing configurations within each flow parameter. Further ahead, research needs to be undertaken to establish the inter-se importance/ weightage of these flow parameters forming up this one airwake component, with respect to their contribution to the Pilot workload. It is possible that a particular flow parameter making up the criteria set, far out-weighs the others in its effect on pilot workload and this aspect accordingly needs further investigation. This will be necessary for making an overall assessment for the airwake component based on a configuration's performance for each of the flow parameters. Also, benchmark numeric values, as discussed above, need to be established for these parameters through experimental/ numerical assessment of a ship-helo


combination for which SHOL trial results have been established as acceptable. Such benchmarks can then be used for acceptance of a newly proposed geometry for the component of airwake.


The quantification process for the various components and establishing their inter-se weightage towards Pilot workload, as proposed above, can be undertaken by effectively employing piloted flight simulations in a parametric investigation with known combinations of various components simulated for a ship helo configuration. In order to remove human error in the qualitative scales, multiple pilots should be made to undertake testing for the same ship-helo configurations. The Pilot effort scales thus generated can be studied in line with the variations of the defining parameters to decide on the inter-se weightage for these parameters. This knowledge can then be translated into fixing numerical limits for the flow parameters for qualifying the ship design for efficient helo operations.


5. 1.


REFERENCES


WHITBREAD, R.E., COLEMAN, S.A., CAA Paper 99004, "Research on Offshore Helideck Environmental Issues", BMT Fluid Mechanics Limited, Document No. 43135 Report 2, Civil Aviation Authority, UK, August 2000, IS 0 86039 786 6.


2.


PRAVEEN, B., VIJAYAKUMAR, R., SINGH, S.N., SESHADRI, V., “A review of the problem of warship helo interaction and efforts underway for possible solutions”, The Royal Institution of Naval Architects International Conference ICSOT- Technical innovation in shipbuilding, 12-13 Dec 2013, Kharagpur, India, pp 163-176.


3.


PRAVEEN, B., VIJAYAKUMAR, R., SINGH, S.N., SESHADRI, V., “Numerical investigation of ship airwake over helodeck for different variants of hangar shapes of generic warship”, The Royal Institution of Naval Architects International Conference on Computational and Experimental Marine Hydrodynamics MARHY 2014, 03-04 Dec 2014, Chennai, India.


4.


ZAN, S.J., SIMS, G.F., CHENEY, B.T., "Analysis of patrol frigate airwakes", RTO AVT Symposium on “Fluid Dynamics Problems of Vehicles Operating near or in the Air-Sea Interface”, Amsterdam, The Netherlands, 5-8 October 1998, published in RTO MP-15.


5.


BOUDA, N.N., SCHIESTEL, R., AMIELH, M., REY, C., BENABID, T., "Experimental approach and numerical prediction of a turbulent wall jet over a backward facing step", International Journal of Heat and Fluid Flow 29 (2008) 927–944, Jan 2008.


6.


BADRI KUSUMA, M.S., RAY, C., MESTEYER, P.G., "The Effects of wall roughness and the external flow structure on


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