Wind and Atmosphere
pg. #
A.6.2.1.4 Atmosphere and Wind Model
In order to accurately predict the trajectory of a launch the simulations need a
atmospheric and wind profile model. This model predicts the conditions a launch vehicle
experiences when traveling through Earth’s atmosphere. Also, the model is used when
predicting the balloon ascension. These conditions determine the various aerodynamic
forces imparted on a moving vehicle. A model of the wind is needed as well. The
simulations need a wind model that realistically simulates the random wind magnitudes
and directions experienced during a flight.
A.6.2.1.4.1 Standard Atmosphere Profiles
The atmosphere model used to run the simulations is based on the standard atmosphere
data based of the 1976 NASA Standard Atmosphere. The simulations use a MATLAB
function called atmosphere4.m. Input into the function is geopotential height. The
function outputs the temperature, density, and pressure at the selected height. The model
makes these calculations up to a height of 89.9 km.
Figures A.6.2.1.4.1.1 through
A.6.2.1.4.1.3 show plots of the pressure, temperature and density outputs from this
function.
Figure A.6.2.1.4.1.1: Standard atmosphere temperature profile.
(Allen Guzik)
Author: Allen Guzik
Wind and Atmosphere
pg. #
Figure A.6.2.1.4.1.2: Standard atmosphere pressure profile.
(Allen Guzik)
Figure A.6.2.1.4.1.3: Standard atmosphere density profile.
(Allen Guzik)
A.6.2.1.4.2 Wind Gusting Algorithm
Another aspect of the wind and atmospheric model is the unpredictable nature of wind
gusts. Within the wind model architecture there is a wing gusting generator. The
concept behind the wind gusting generator is to be able to generate random wind gusts
then add them to the constant wind profile.
Author: Allen Guzik
Wind and Atmosphere
pg. #
There are many parameters designed into the gusting algorithm to allow for random
gusting. First, unique to each launch, we choose the number of gusts a vehicle can
experience. This number is random and can vary from 0 to 20 gusts per launch. Another
unique property to each launch is the altitude in the atmosphere where each gust occurs.
Each gust is assigned a random altitude where the gust happens. The possible altitude
range is from 0 km to 30 km.
The direction of each gust is also random for each gust. This allows for the unpredictable
nature of the wind changing direction. The direction is selected to always be parallel to
the ground. This means the model does not generate any up or down drafts. Each gust
direction is in any direction that is plus or minus 90˚ from the direction of the constant
wind profile.
The last component of the wind gust algorithm is the magnitude of each gust. Each gust
has a random magnitude that can be anywhere between 0 m/s to 12 m/s. This magnitude
is added to the constant wind profile. For example; if a gust of 9 m/s is assigned to the
altitude of 10 km and is going in exactly the same direction of the constant wind the
resulting wind is: At that altitude, the constant wind is 40 m/s. The resulting total wind
velocity is 49 m/s. Lastly, concerning the magnitude of the wind gust, is the duration of
each gust. The gust is modeled such that the gust is an impulse. This decision is based
off of assuming the length of altitude each gust is small enough that when considering the
velocity of the rocket traveling through that altitude range, the gust acts as an impulse.
An example of a possible wind profile generated from AAE450_wind_model.m with
gusts for a ground rocket launch is provided in Figures A.6.2.1.4.2.1 and A.6.2.1.4.2.2.
Author: Allen Guzik
Wind and Atmosphere
pg. #
Figure A.6.2.1.4.2.1: Example of a wind profile with gusting in the north/south direction.
(Kyle Donahue and Allen Guzik)
Figure A.6.2.1.4.2.2: Example of a wind profile with gusting in the East/West direction.
(Kyle Donahue and Allen Guzik)
Author: Allen Guzik