analysis of wind shear for the exomars mission using ultra-high resolution large eddy simulation...
DESCRIPTION
Objectives Evaluate wind shears at ExoMars landing site Definition: A strong wind shear at an atmospheric level results either from large differences of wind amplitude or contrasts in wind direction, or both, over a small vertical extent.TRANSCRIPT
Analysis of wind shear for the ExoMars missionusing ultra-high resolution Large Eddy Simulation
T. Bertrand, A. Spiga, A. Colaïtis
Mission contextExoMars ESA mission 2016:
- TGO- EDM
Landing point: Meridiani Planum ̴ 1.88°S / 353.87E
Objectives Evaluate wind shears at ExoMars landing site
Definition:
A strong wind shear at an atmospheric level results either from large differences of wind amplitude or contrasts in wind direction, or both, over a small vertical extent.
Objectives
Wind shear
Evaluate wind shears at ExoMars landing site
Possible effect of a wind shear on EDM’s landing system:
Large Eddy Simulation:
400 levels between 0 and 5 km altitudeVertical resolution =12.5 mLCT = 1 p.m until 1.45 p.m
Horizontal resolution = 12 m
Wind shear characterization
Wind vector
U
V
θUV (alt = n+1)
UV (alt = n)
Δ(θ)
D(UV)
D(UV) enables to evaluate the combined effects of angle and amplitude. It is a good indicator of wind shears.
√𝑈 ²+𝑉 ²
U
V
Vertical discretization
12.5 m12.5 m12.5 m
UV (m/s)
Altitude (m)
1 3 6 7
In order to constrain the mission, we are concerned with wind shears occuring over a vertical distance of 20-30 m
with UV and θ profiles
Exemple of wind shears
Altit
ude
(km
)
Δ(UV) Δθ(°)
Wind shear with high Δ(UV)
Wind shear with high Δθ
Δ(UV) and Δ(θ) at 4 different times and at two different locations (distant from 750m)
Between 0-5 km and 0100PM-0145PM
Maximal values of D(UV)
D(UV) [ s-1 ]
Δ(UV) Δθ
Extreme cases of wind shear profiles
Red curve: sheared caseBlue curve: smooth case
Altit
ude
(km
)
D(UV)
High Δθ
D(UV)= 0.42 s-1 (15.7 m.s-1 over 37,5m)
Probability of wind shearConsidering maximal values of D(UV) only
(s-1)
max
Probability of wind shearConsidering all values of D(UV) from LES
(s-1)
max
Conclusions• Wind shears diagnostic D(UV) … combining gradient of wind
amplitude and wind direction.
• Most plausible ExoMars landing profiles have very moderate shears (< 3 m.s-1 over a vertical distance of 37.5 m).
• A majority of maximal shears are between 0.15 and 0.25 s-1.
• Extreme wind shears of about 15 m.s-1 are found over a vertical distance of 37.5 m (but low probability: P < 0.01).
• On the one hand, the probability of having wind shears less than 0.1 s-1 is quite high when considering all times and altitudes available. When considering only maximal wind shears over the same area, a majority of wind shears between 0.15 and 0.25 s -1 are found. In a general way, over a vertical distance of 37.5 m, variations of wind amplitude of 3 m.s -1 combined with angle variation of about 60° are relatively frequent.