Experimental And Numerical Study On Wind And Fire Fields On Aircraft Carrier Deck

The aircraft carrier deck is crowded with staff,aircrafts,weapons,equipments,the corresponding mobilization and coordination are extremely complex.Thus,aircraft carrier deck is known as the most dangerous man-made environment,especially for the landing of carrier-based aircraft,which is called as the dance on the tip of the knife,accounting for 80%of aircraft carrier safety accidents.The failure of landing will not only destroy the aircraft itself,but also cause serious damage to other carrier aircrafts,equipments and staff.In order to reduce the sway of the carrier,the landing of carrier-based aircraft must maintain a certain speed.Even when the sea is calm,there is still a relative wind speed.In windy conditions,carrier usually cruise against the wind to avoid tangential velocity.All of these will cause the airflow to bypass the carrier and form airwake.Airwake will cause unpredictable changes in the landing process,which has a great impact on landing safety.Once an aircraft crashes and causes a fire,the deck wind will aggravate the fire.The ammunition and the fuel leaked from the surrounding aircrafts will be ignited quickly,resulting in more serious secondary accidents.Aiming at the typical aerodynamic and fire dynamics problems in the landing process of carrier-based aircraft,the landing process is decomposed into the weak coupling between airflow field and descending process of carrier-based aircraft and the coupling between airflow field and deck fire.The main contents and conclusions are as follows.Firstly,because of the complex three-dimensional shape of the carrier,it is difficult to evaluate the calculation results of the airflow field.The cube model can be used instead of the carrier model.Because its anisotropic characteristics is similar to the carrier and it is easy to carry out quantitative analysis for its similarity.The different characteristics of the eight methods are comprehensively evaluated in terms of the distribution of turbulent kinetic energy,the length of vortices at the top and the location of wake reattachment points.The numerical method with the best accuracy and economy is defined,and DES model is selected as the optimal scheme for the simulation of ship airwake.In addition,through PIV wind tunnel experiments and numerical calculations,it is clear that the atmospheric boundary layer on the sea surface has significant impact on the flow field around a cube.It results in the downward movement of the pressure distribution center on the windward side,the enlargement of the maximum turbulent kinetic energy distribution area and the lengthening of the recirculation area.Extended this rule to the ship,the atmospheric boundary layer will lead to the deterioration of the airwake.Secondly,the applicability and economy of hexahedron structured grid,tetrahedron and polyhedron unstructured grid are discussed by the numerical simulation of simplified destroyer model 2(SFS2).In order to control the slenderness ratio of structured grids,when the height of the first layer is small,the grid length must be limited,which leads to a large number of structured grids.The number of polyhedral meshes is only less than 1/3 of tetrahedral meshes and about 1/2 of hexahedral meshes under the same accuracy.Using polyhedral mesh and DES turbulence model,the unsteady flow field of Nymez carrier CVN-71 is simulated.The average velocity distributions of typical cross-section,the average velocity curves of slide line,the velocity fluctuation curves of monitoring points near the deck surface,and the power spectral density analysis are given.The shedding of bow vortices is observed.According to the weak coupling results,it is found that the airwake will lead to the reduction of the airspeed,the increase of the low speed and the increase of the track inclination of the uncontrolled aircraft.All these factors lead to the aircraft landing 11 meters ahead of the ideal landing point.In this paper,both experimental and numerical methods are used to study kerosene pool fire.The open cup flash point,flame spreading speed,heat release rate and combustion heat of kerosene were measured by experiments.In addition,five large-scale kerosene pool fires with different areas of 0.5m2?1m2?2m2?5m2.10m2 were carried out.The mass burning rates of pool fires in different areas as well as the plume characteristics including flame height,pulsation frequency,radial spread velocity were obtained.The flame center line temperature,smoke concentration and heat flux at specific location were also measured.The formulas of mass burning rate,flame height,fluctuating frequency and heat flux varying with oil pool diameter,and the formula of flame center temperature varying with flame height are given.The burning rate does not change with the increase of the diameter after the oil pool size exceeding 10m2,which is an important theoretical basis for the larger-scale numerical simulation of pool fire.Finally,based on the experimental data and rules,a numerical simulation method for large-scale kerosene pool fire is proposed and the consistency of the numerical simulation method is verified by experimental results.Fire plume inclines in the presence of wind.The characteristic parameters and theoretical formulas of inclined flame are given based on literatures.The simulation of 100m2-400m2 pool fire at 15 and 30 knot wind speed were carried out and compared with the theoretical method.In addition,the 400 m2 fire source was placed on the deck of the CVN-71 aircraft carrier.The center of fire source coincided with the ideal landing point.The coupling simulation of the airflow field of aircraft carrier with the thermal buoyancy field of large-scale pool fire were carried out.The isoline of heat flux distribution is given,and the dangerous range of deck under 15 and 30 knots of wind speed is evaluated with the criterion of thermal radiation damage.