Trying to understand the changes in bird modelling parameters at sea level and 8000 ft altitude for a bird strike. I have modelled a 4lb bird in LSDYNA using SPH Lagrangian technique using MAT_NULL material properties and linear polynomial EOS with 10% porosity as shown in Table 1. Bird impact velocity (V) is 180m/s at sea level and 0.85V at 8000 ft altitude as per certification requirements.
Known fact that air density decreases with altitude, which makes the bird move faster at higher altitude due to low air density as compared to the sea level. Whereas, air viscosity increases with altitude as temperature decreases. Q1. How to model air medium around bird SPH model in LSDYNA bird strike analysis? Q2. Does these change in air properties (density and viscosity) between sea level and 8000 ft produce major change in bird strike results?
In addition, since bird is modelled as 95% water with density 950 Kg/m3, the dynamic viscosity of water changes with altitude. Q3. Is there any other bird parameters change with altitude, say at 8000 ft? Q4. What about control bulk viscosity for the shock phenomenon?
Table 1: Bird impact properties
Bird Material Properties
Mass Density =950 Kg/m3 = 8.89E-05 lbf.s2/in4
Pressure Cutoff = -9.97E+04 Pa = -14.5 psi
Dynamic Viscosity Coeff = 0.0027 pa.s = 3.916E-07 psi.s
EOS parameters
C1 = 28 Mpa = 4.06 Ksi
C2 = -85 Mpa = -12.3 Ksi
C3 = 35000 Mpa = 5076 Ksi
Control Bulk Viscosity
Quadratic viscosity coefficient (Q1)= 2 N.s/m2 = 2.90E-04 lb.s/in2
Linear viscosity coefficient (Q2) = 0.25 N.s/m2 = 3.63E-05 lb.s/in2
Dear Paul,
As per some of your questions, I would say:
Q1) How to model air medium around bird SPH model in bird strike analysis?
I recommend you to use the International Standard Atmosphere (ISA)
Q2) Does these change in air properties (density and viscosity) between sea level and 8000 ft produce major change in bird strike results?
My guess is that, rather than these changes in air properties, it has a much stronger impact on the bird strike results the much higer flight speed of aircraft at higher altitudes, compared with floght speed at sea level (SL)
Q3) Is there any other bird parameters change with altitude, say at 8000 ft?
The bird impact will likely be quite different (direction and location of the impact on the aircraft) depending on whether it is at SL or high altitudes, because of the flight phase and aircraft flight conditions, attitude, etc., at SL and 8000 ft.
Hope this is useful,
Sincerely,
Jose Ignacio Rojas Gregorio Thank you for your answer. Q1) I meant how to model the air surrounding the bird part in LSDYNA. Q2) I agree that bird velocity have higher effect on the impact force or pressure. But does that mean, can I ignore the high altitude air and water properties variations at 8000 ft?
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