Research On Quantitative Quality Evaluation And POD Reconstruction Of Ship Deck Airflow Field

Ships are under the influence of many complex factors,such as the geometric shape of the ship,the intensity and direction of the natural wind,the turbulence component of the free flow,the sea condition and the ship's navigation.As the carrier-based aircraft and the high precision electronic equipment are widely assembled on modern ships,the complex external factors and the various superstructure forms on the surface of the ship deck have resulted in the very strong instability and high complexity of the space flow field above the deck.The change of any one factor may cause a key change in the space flow field above the ship deck,and often we need to make a decision based on the ship surface flow field to determine whether the ship equipment on ship surface and the carrier-based aircraft can run safel,and the qualitative method is not able to solve this problem.Therefore,it is necessary to evaluate the overall quality of ship's surface flow field from a qualitative and quantitative point of view.Through quantitative method,the overall quality of the ship surface flow field can be ordered,and the key point of the optimal and worst flow field can be obtained by a certain processing method.These key points have the greatest impact on the flow field in a certain sense.In real ship operation,we can detect the changes of these key points to judge the changes of the quality of the flow field and make various decisions.This paper introduces the numerical simulation calculation method and solution scheme,and verification of the reliability of the calculation method.The flow field of ship deck surface under different conditions(wind direction 0 to 180 degrees,wind direction interval 15 degrees,wind speed 10m/s to 25m/s,and wind speed interval 5m/s)is solved.First,the airflow,turbulent kinetic energy distribution,pressure distribution and helicity distribution are analyzed.The results show that the shedding vortex of the hull edge of the ship's bow and the ship's stern hangar and the tail vortex at chimney's back side formed by the airflow flow around SFS2 chimney will be mixed in the stern,making the space above the stern apron in the large scale vortex under low wind direction(0 to 30 degrees).And under the high wind direction(45 To 135 degree),the airflow is impacted on the SFS2 starboard,and the airflow is washed.There is a large scale turbulent energy over limit zone at the intersection of the high speed air flow and the large low velocity airflow vortex in the back air side of the ship.At the wind direction from 135 to 180 degrees,the ship stern apron gradually deviates from the shedding vortex on the edge of the hull,and some area is divided by the air flow on the edge of the deck.With the increase of relative wind speed,the ship's surface high and low pressure areas and turbulent kinetic energy overrun areas increase with the increase of relative wind speed.Secondly,the quantitative quality evaluation model of the ship surface flow field is established,and the TOPSIS(Technique for Order Preference by Similarity to an Ideal Solution)method is used to order the quality of the SFS2 ship surface flow field under different working conditions.The results show that the quality of the SFS2 surface flow field is relatively high in low wind speed conditions,and the overall quality of the flow field of the SFS2 is relatively low at high wind speed(the overall quality of flow field:realtive wind speed 10m/s>20m/s>15m/s>25m/s),and the greater the lateral wind,the lower the quality of the ship surface flow field.Finally,POD(Proper Orthogonal Decomposition)is used to reconstruct the flow field of 0,30,90 and 150 degree of SFS2 ship surface with relative wind speed 15m/s,and the difference of the flow field of SFS2(Simple Frigate Shape)before and after POD reconstruction is compared and analyzed,and the key features of the ship surface flow field are extracted.