**7. Rover vehicle aerodynamics**

The external surface of rover is not designed following aerodynamics criteria. The main body of this vehicle is a box with rectangular section, supported by six wheels. A vertical mast is erected on the upper surface of the main box body. The instruments of MEDA are installed over this mast. Two booms are located perpendicular to the axis mast. The rover vehicle is larger than other elements as mast and booms, and the flow viewed by small devices is mainly affected by the presence of the rover.

The flow visualization is a qualitative technique that offers a global view of the flow so that it provides a first approximation to the study of the flow. **Figure 9** shows the smoke visualization at low Reynolds number when the flow was illuminated by a laser light sheet. This experiment was performed in a small commercial wind tunnel from TSI (model 8390) installed in our laboratory. It was running at an airspeed of 2.6 m/s. This tunnel has a square cross test section of 100 100 mm<sup>2</sup> with transparent walls, in order to provide optical access for the recording camera. The smoke was produced by burning incense bars.

**Figure 11** shows the averaged velocity map in a vertical plane of the flow containing the boom 1 of the rover, when the flow was blowing with zero angle of incidence and airspeed of 10 m/s coming from left to right. The color scale represents the velocity magnitude in meter per second. The deflection of streamlines can be observed near the boom 1, although the flow is attached. On the other hand, the flow in the wake of the mast is detached and enclosed in a low-velocity recirculation

**Figure 12** shows the averaged velocity map in a horizontal plane of the flow containing both booms 1 and 2, because they are installed at the same height over the mast. No symmetric deflection of streamlines is observed. This effect is due to the presence of the rover central box and the vertical mast, which is located in the right side of the rover. Flow is coming from left to right and the mast wake is clearly visible, with low velocities (blue color). The wind sensor 2 (WS2) is located as an

The flow over the rover was investigated at low Reynolds number (6770) by wind tunnel testing a small rover model with a characteristic length of 38 mm (scale 1: 45th). A TSI model 8390 wind tunnel specially adapted to very low flow velocities was used (mean airspeed of 2.6 m/s). This tunnel has a square cross test section of

*).*

*).*

bubble.

**Figure 11.**

**Figure 12.**

**81**

appendix forming 120° with camera axis.

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

*Velocity map in a vertical plane (Re = 2.2 105*

*Top view: Velocity map of a horizontal plane (Re = 2.2 105*

The flow is coming from right to left. Photo in left-hand side shows the streamlines of flow when curved by the presence of the mast and the camera, and a detached flow is produced downstream. On the other hand, photo in right-hand side shows the flow when coming from rear of the rover. The flow is deviated by effects of a large box that corresponds to the module of MMRGT and a detached stream is produced behind this module. Only some streamlines are coming to the camera height but curved.

**Figure 10** shows the smoke visualization carried out in the INTA-1 wind tunnel. This facility has maximum airspeed of 60 m/s and closed circuit with open test section of 2 3 m2 . The flow around the rover was running at high Reynolds number and it was illuminated by conventional white light. The flow is steered to the rover presence forming a fine smoke tube, but the direction of the smoke is slightly deflected as it is coming to the rover vehicle rising the boom 1 with an angle different to zero as corresponds to no disturbed horizontal flow, which is the effect of the presence of the rover. The direction of the wind received by sensors is changed by the rover presence. Flow is coming from right to left.

The quantitative analysis of the flow was performed by means of Particle Image Velocimetry (PIV). This is a nonintrusive technique that illuminates the flow seeded with tracer particles and provides simultaneously, the flow field velocity in a plane of the flow [13].

**Figure 9.** *Smoke visualization of flow around rover (Re = 6770).*

**Figure 10.** *Smoke visualization of flow around rover (Re = 2.2 105 ).*

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

The flow visualization is a qualitative technique that offers a global view of the flow so that it provides a first approximation to the study of the flow. **Figure 9** shows the smoke visualization at low Reynolds number when the flow was illuminated by a laser light sheet. This experiment was performed in a small commercial wind tunnel from TSI (model 8390) installed in our laboratory. It was running at an airspeed of 2.6 m/s. This tunnel has a square cross test section of 100 100 mm<sup>2</sup> with transparent walls, in order to provide optical access for the recording camera.

The flow is coming from right to left. Photo in left-hand side shows the stream-

**Figure 10** shows the smoke visualization carried out in the INTA-1 wind tunnel.

The quantitative analysis of the flow was performed by means of Particle Image

*).*

Velocimetry (PIV). This is a nonintrusive technique that illuminates the flow seeded with tracer particles and provides simultaneously, the flow field velocity in a

. The flow around the rover was running at high Reynolds

This facility has maximum airspeed of 60 m/s and closed circuit with open test

changed by the rover presence. Flow is coming from right to left.

number and it was illuminated by conventional white light. The flow is steered to the rover presence forming a fine smoke tube, but the direction of the smoke is slightly deflected as it is coming to the rover vehicle rising the boom 1 with an angle different to zero as corresponds to no disturbed horizontal flow, which is the effect of the presence of the rover. The direction of the wind received by sensors is

lines of flow when curved by the presence of the mast and the camera, and a detached flow is produced downstream. On the other hand, photo in right-hand side shows the flow when coming from rear of the rover. The flow is deviated by effects of a large box that corresponds to the module of MMRGT and a detached stream is produced behind this module. Only some streamlines are coming to the

The smoke was produced by burning incense bars.

camera height but curved.

*Mars Exploration - A Step Forward*

section of 2 3 m2

plane of the flow [13].

*Smoke visualization of flow around rover (Re = 6770).*

*Smoke visualization of flow around rover (Re = 2.2 105*

**Figure 9.**

**Figure 10.**

**80**

**Figure 11** shows the averaged velocity map in a vertical plane of the flow containing the boom 1 of the rover, when the flow was blowing with zero angle of incidence and airspeed of 10 m/s coming from left to right. The color scale represents the velocity magnitude in meter per second. The deflection of streamlines can be observed near the boom 1, although the flow is attached. On the other hand, the flow in the wake of the mast is detached and enclosed in a low-velocity recirculation bubble.

**Figure 12** shows the averaged velocity map in a horizontal plane of the flow containing both booms 1 and 2, because they are installed at the same height over the mast. No symmetric deflection of streamlines is observed. This effect is due to the presence of the rover central box and the vertical mast, which is located in the right side of the rover. Flow is coming from left to right and the mast wake is clearly visible, with low velocities (blue color). The wind sensor 2 (WS2) is located as an appendix forming 120° with camera axis.

The flow over the rover was investigated at low Reynolds number (6770) by wind tunnel testing a small rover model with a characteristic length of 38 mm (scale 1: 45th). A TSI model 8390 wind tunnel specially adapted to very low flow velocities was used (mean airspeed of 2.6 m/s). This tunnel has a square cross test section of

**Figure 11.** *Velocity map in a vertical plane (Re = 2.2 105 ).*

**Figure 12.** *Top view: Velocity map of a horizontal plane (Re = 2.2 105 ).*

<sup>100</sup> � 100 mm<sup>2</sup> with transparent walls of methyl methacrylate. It provides optical access for experimental techniques and visual access to the experimentalist.

Laser Doppler Anemometry (LDA) is a punctual nonintrusive measurement technique that is usually used to investigate the flow field velocity with very high accuracy and resolution [14].

**Figure 13** shows the experimental set-up, with a body axes system fixed to the model. The angle of wind incidence is defined as *β*, and the location of both booms is indicated, and the orientation of the LDA probe remains fixed while the model is turning on to simulate different incident wind angles.

LDA measurements were carried out by using a commercial system from Dantec. The illumination source consists of a 10 mW He-Ne laser beam emitting in red color (wavelength of 632.8 nm). A BSA-F60 Flow Processor and BSA Flow software provide data of flow velocity. Seeding particles were produced by means of a water ultrasonic atomizer. **Figure 14** shows the rover model inside the wind tunnel test section during the test experiments and measuring velocity by LDA. Rover vehicle was supported by a circular plate that facilitates the rover turn on during test campaign. Reflexions of red LDA laser beam can be observed in the walls of wind tunnel test chamber.

Modulus of wind velocity in sensor 1 location is determined from three orthogonal velocity components measured by LDA after the following expression:

$$\mathbf{V\_1 = \sqrt{\mathbf{U\_{LDA}^2 + V\_{LDA}^2 + W\_{LDA}^2}}}.\tag{40}$$

On the other hand, measurements provided by both sensors in the cut-off angles (30, 105, 120, and 240°) are valid, and the wind velocity in these points would be

**Figure 16** shows forbidden circular sectors for both wind sensors measurements. When wind is blowing from forbidden angles of incidence, the flow is detached by a combined effect of the camera mast and MMRGT of rover that produce a turbulence flow in the mast wake that is coming to the booms where the rover wind sensors are installed. Graphs in **Figure 16** demonstrate that complete circular angles

Finally, the velocitymeasured by each wind sensormust be corrected from the effects

where *Ki* is the calibration factor that must be determined for each sensor, from

*VW* ¼ *KiVi*; *i* ¼ 1, 2 (41)

*:* (42)

of the external geometry of the rover vehicle. The true wind velocity *VW* is given by

data contained in **Figure 15**, by computing calibration factors by the following

*Ki* <sup>¼</sup> *VW Vi*

range can be measured by the combination of both wind sensors.

determined by an averaged velocity value.

*Wind velocity measured by rover booms.*

*Rover model inside the test section during LDA measurements.*

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

expression:

**83**

**Figure 14.**

**Figure 15.**

An analogous expression was used to compute the velocity at the location of sensor 2.

**Figure 15** shows the modulus of velocity as seen by both wind sensors WS1 and WS2. Differences with freestream velocity are observed in wind velocity detected by laser Doppler in respective locations of rover wind sensors. Velocities were measured for different incidence wind angles in range 0–360°. Two forbidden bands that correspond to not valid data are marked in **Figure 15**. These areas correspond to detached flow when the sensors are located mainly in the wake of camera mast and MMRGT of rover. In practice, the solution is to use active operating redundancy, since both sensors are operating simultaneously in order to complement the forbidden regions, so that whole angular sector can be measured by rover sensors.

The sensor 1 (WS1) is the main sensor because this sensor will be used for wind measurements except in the not valid region. The sensor 2, named as WS2, must be used in the forbidden band of sensor 1.

**Figure 13.** *Top view: Velocity map of a horizontal.*

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

<sup>100</sup> � 100 mm<sup>2</sup> with transparent walls of methyl methacrylate. It provides optical access for experimental techniques and visual access to the experimentalist. Laser Doppler Anemometry (LDA) is a punctual nonintrusive measurement technique that is usually used to investigate the flow field velocity with very high

**Figure 13** shows the experimental set-up, with a body axes system fixed to the model. The angle of wind incidence is defined as *β*, and the location of both booms is indicated, and the orientation of the LDA probe remains fixed while the model is

Modulus of wind velocity in sensor 1 location is determined from three orthog-

An analogous expression was used to compute the velocity at the location of sensor 2. **Figure 15** shows the modulus of velocity as seen by both wind sensors WS1 and WS2. Differences with freestream velocity are observed in wind velocity detected by laser Doppler in respective locations of rover wind sensors. Velocities were measured for different incidence wind angles in range 0–360°. Two forbidden bands that correspond to not valid data are marked in **Figure 15**. These areas correspond to detached flow when the sensors are located mainly in the wake of camera mast and MMRGT of rover. In practice, the solution is to use active operating redundancy, since both sensors are operating simultaneously in order to complement the forbidden regions, so that whole angular sector can be measured by rover sensors.

The sensor 1 (WS1) is the main sensor because this sensor will be used for wind measurements except in the not valid region. The sensor 2, named as WS2, must be

*LDA* <sup>þ</sup> *<sup>V</sup>*<sup>2</sup>

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

*LDA* <sup>þ</sup> *<sup>W</sup>*<sup>2</sup>

*LDA*

*:* (40)

onal velocity components measured by LDA after the following expression:

*U*2

q

LDA measurements were carried out by using a commercial system from Dantec. The illumination source consists of a 10 mW He-Ne laser beam emitting in red color (wavelength of 632.8 nm). A BSA-F60 Flow Processor and BSA Flow software provide data of flow velocity. Seeding particles were produced by means of a water ultrasonic atomizer. **Figure 14** shows the rover model inside the wind tunnel test section during the test experiments and measuring velocity by LDA. Rover vehicle was supported by a circular plate that facilitates the rover turn on during test campaign. Reflexions of red LDA laser beam can be observed in the

accuracy and resolution [14].

*Mars Exploration - A Step Forward*

walls of wind tunnel test chamber.

used in the forbidden band of sensor 1.

**Figure 13.**

**82**

*Top view: Velocity map of a horizontal.*

turning on to simulate different incident wind angles.

*V*<sup>1</sup> ¼

**Figure 14.** *Rover model inside the test section during LDA measurements.*

**Figure 15.** *Wind velocity measured by rover booms.*

On the other hand, measurements provided by both sensors in the cut-off angles (30, 105, 120, and 240°) are valid, and the wind velocity in these points would be determined by an averaged velocity value.

**Figure 16** shows forbidden circular sectors for both wind sensors measurements. When wind is blowing from forbidden angles of incidence, the flow is detached by a combined effect of the camera mast and MMRGT of rover that produce a turbulence flow in the mast wake that is coming to the booms where the rover wind sensors are installed. Graphs in **Figure 16** demonstrate that complete circular angles range can be measured by the combination of both wind sensors.

Finally, the velocitymeasured by each wind sensormust be corrected from the effects of the external geometry of the rover vehicle. The true wind velocity *VW* is given by

$$V\_W = K\_i V\_i; i = \mathbf{1}, \mathbf{2} \tag{41}$$

where *Ki* is the calibration factor that must be determined for each sensor, from data contained in **Figure 15**, by computing calibration factors by the following expression:

$$K\_i = \frac{V\_W}{V\_i}.\tag{42}$$

**Nomenclature**

*E*2

*A* transversal area of body boom *Aw* area of heat transfer for the wire

*a* radius of the boom *C* empirical coefficient *C1* empirical coefficient *D* empirical coefficient *D1* empirical coefficient *d* wire diameter *E* energy of wire

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

*<sup>W</sup>* voltage of the wire

*k* conductivity of fluid

*n* empirical coefficient

*Re* Reynolds number *RCO2* constant of CO2 gas *Rg* constant of gas fluid *S* reference temperature *Tw* wire temperature *T*<sup>∞</sup> flow temperature *u* flow velocity component *U*<sup>∞</sup> freestream velocity

*v* flow velocity component

*V* flow velocity j j *V* modulus of velocity

**Greek symbols**

**85**

*VW* true wind velocity

*λ* mean free path

*Φ* velocity potential

*Ψ* stream function

*ρ* density

*W* heating power of wire

*Kn* Knudsen number

*h* thermal convection coefficient *I* electric intensity crossing the wire

*Ki* calibration factor of velocity

*Nu* nondimensional Nusselt number *Q* transferred heat to the flow *R* electric resistance of the wire

*M* strength of a three-dimensional point source

*ULDA* velocity component measured by LDA after *x* axis of rover

*VLDA* velocity component measured by LDA after *y* axis of rover

*WLDA* velocity component measured by LDA after *z* axis of rover

*V1* wind velocity measured in location of boom 1.

*μ* dynamic viscosity coefficient of the fluid *ν* kinematic viscosity coefficient of the fluid

*L* characteristic length scale

*g* gravity

**Figure 16.** *Forbidden circular sectors for wind sensors measurements.*

This ratio is precisely the inverse of this presented in **Figure 15** and it represents the effect of rover vehicle over the booms.

#### **8. Conclusions**

The Mars 2020 rover aerodynamics plays a fundamental role in the operation of rover wind sensors. A set of hot film sensors have been specially designed to be installed over two booms located perpendicular to camera mast of rover. This kind of sensors are based on the heat transfer from sensors to environment around the sensors, but physical properties of Earth atmosphere are very different to these present in Mars atmosphere where sensors will operate during Mars 2020 mission.

Reynolds number is the fundamental parameter to establish the physical similarity between real flow in Mars and this investigated in Earth by wind tunnel testing.

Potential flow provides a first approximation to study the longitudinal and transversal flows over booms where wind sensors will be installed. Limitations of the potential model are evidenced by detachment flow in the wake of booms with transversal flow and the presence of the boundary layer where viscous effects are of the same order of inertial effects. Due to these limitations, a more intensive experimental investigation is necessary. Global information about the flow pattern around the rover vehicle was obtained by smoke visualization. Qualitative techniques as Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) were used to get insight about the velocity field. The effects of rover vehicle over the flow coming to the sensors booms were studied, and not valid regions of each sensor were determined.

Finally, the calibration factor equation was indicated as the main way to correct flow velocity from the adverse effects produced by the rover vehicle over wind sensors measurements.

#### **Acknowledgements**

This investigation was funded by Spanish Ministry of Defense under the program "IGB 99001 Termofluidodinámica" of INTA (National Institute for Aerospace Technology of Spain).

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*
