Erin M. Reed

Investigation of the Interactions of Reaction Control Systems with Mars Science Laboratory Aeroshell

Interactions between the Reaction Control System (RCS) jets and the bow shock from the aeroshell of a Mars Science Lab (MSL) model are investigated. Images are obtained experimentally at the University of Virginia using a low-density, hypersonic wind tunnel with the Planar Laser Induced Iodine Fluorescence technique. The models are .44% MSL aeroshells fitted with 0.5 mm RCS orifices to simulate Reaction Control Systems in both parallel and transverse jet directions relative to the aeroshells. Experiments are conducted at Mach 12 in the underexpanded jet freestream flowfield with sonic RCS jets. Images for both transverse and parallel jets are obtained for nozzle-thrust coefficients ranging from 0 to 3. It is found that there is much interaction between the aeroshell bow shock and the RCS jet for the transverse jet cases; however, there was not much interaction between the parallel jet and the bow shock on the aeroshell. Results from a nozzle-thrust coefficient of 0.5 were compared to numerical simulations for similar conditions obtained using CFD at the University of Michigan. It is found that there is good agreement in flowfield density between the experimental and numerical results in the jet core of the RCS but greater differences near the jet boundaries.

Interactions of Single-Nozzle Sonic Propulsive Deceleration Jets on Mars Entry Aeroshells

The effects of the propulsive decelerator (PD) jet Mach number on the flowfield, surface, and aerodynamic properties of a Mars entry aeroshell are investigated in Mach 12 laminar fl ow of I 2-seeded N2 gas. This is achieved using the computational fluid dynamics (CFD) code LeMANS, as well as the planar laser-induced iodine fluorescence (PLIIF) experimental technique. The results show that the flowfield features, such as the standoff distance of the bow and jet shocks, are all affected by the PD jet Mach number. The results also show that as the thrust coefficient increases, the flow around the aeroshell approaches a jet-only, no freestream configuration due to a PD jet shield. Therefore, the effects of the PD jet Mach number on the surface properties and the drag coefficient increases. As a result, the difference in the drag coefficient between the supersonic and sonic jets increases to as much as 25%. However, since the drag is inversely proportional to the nozzle thrust, the total axial forces for the supersonic and sonic jets are in close agreement, with a maximum difference of 4%. This result indicates that the overall deceleration performance of the aeroshell is only slightly affected by the PD jet Mach number for these particular conditions. The study also shows that propulsive deceleration with central PD jets may only be beneficial for thrust coefficients greater than 1.5 for both sonic and supersonic jets; a result that appears to be independent of the jet exit Mach number. Finally, qualitative comparisons between LeMANS and PLIIF show overall good agreement in the bow shock profile and standoff distance.

Numerical study of hypersonic wind tunnel experiments for Mars entry aeroshells

The combination of landing future high mass systems with small landing footprints on Mars may require the use of both propulsive deceleration (PD) and reaction control system (RCS) thrusters. However, the interactions between these jets and the supersonic or hypersonic freestream involve complex flow phenomena that are still not well understood. This paper describes numerical and experimental techniques that are used in an effort to develop physically accurate methods to compute these complex flow interactions. The paper also presents a numerical parametric study that is conducted using the computational fluid dynamics (CFD) code LeMANS. This study examines the effects of low temperature and density values and radially nonuniform freestream conditions in the hypersonic wind tunnel facility using an aeroshell based on the Mars Science Laboratory in Mach 12 flow of nitrogen gas with PD and RCS jets off. It is shown that although the Blottner and the Sutherland models compute different values of viscosity at low temperatures, the flowfield and surface properties predicted by LeMANS using these two models are in very close agreement. The study also shows that thermal nonequilibrium effects are negligible. The radial freestream nonuniformities, however, have considerable effects on the flowfield and surface properties. The nonuniform conditions change the temperature and density distributions in most of the computational domain, widen the bow shock around the aeroshell, increase continuum breakdown regions, and decrease the drag coefficient of the capsule compared to the uniform conditions. Finally, the paper presents qualitative experimental comparisons with the computed results which show overall good agreement.

Propulsion Deceleration Studies Using Planar Laser-Induced Iodine Fluorescence and Computational Fluid Dynamics

Future high-mass spacecraft entering the thin Martian atmosphere will require additional means of deceleration prior to deploying supersonic parachutes. Propulsive deceleration is one technology that is being considered. The interaction of the spacecraft aerodynamics with the propulsion deceleration (PD) jets has been shown to cause a decrease in drag coefficient with increasing thrust coefficient, which is not desirable for deceleration. Planar LaserInduced Iodine Fluorescence (PLIIF) images showed a lifting of the vehicle bow shock away from the aeroshell. Flowfield calculations performed using a CFD code showed that this lifting was responsible for the decrease in drag with increasing PD jet thrust. With 4 PD jets located midway between the aeroshell centerline and shoulder, PLIIF images showed that the vehicle bow shock is maintained between the jets as the thrust coefficient is increased. CFD calculations established that this bow shock was responsible for greater drag preservation with the peripheral jets. The peripheral jet drag coefficient was 4 times larger than the single jet value at a thrust coefficient of 2.0. The calculations also showed low pressure wakes located radially behind the peripheral jets which are responsible for the decrease in drag coefficient with increasing thrust coefficient and that high pressure is maintained between the jets. These results suggest that using a few peripheral PD jets located near the aeroshell shoulder would provide the greatest amount of drag preservation when using propulsive deceleration. Nomenclature

Investigations of Peripheral 4-Jet Sonic and Supersonic Propulsive Deceleration Jets on a Mars Science Laboratory Aeroshell

With the launch of Mars Science Laboratory (MSL), scheduled for 2011, Viking technology developed in the 1970s is reaching its limits for entry, descent and landing (EDL) on Mars, necessitating research and development of other technologies for decelerating high mass Mars entry systems (HMMES), such as propulsive deceleration (PD) jets. In this paper planar laser-induced iodine fluorescence is utilized to obtain qualitative flow visualization images and quantitative PD jet mole fraction images of peripheral sonic and supersonic PD jet models in Mach 12 flow and compared to CFD computations. The models are 0.22% of the MSL frontal area, with Mach 1 and Mach 2.66 jets on the frontal aeroshell of the model, oriented normal to the hypersonic flow. The interactions of PD jets with a Mach 12 freestream flow are visualized with coefficients of thrust (CT) varying from 0.5 to 3.0 in increments of 0.5. It was found that as CT increases the shock stand-off distance increases for both sonic and supersonic cases, with the supersonic distance at a CT = 3.0 being 17% greater than the sonic distance. The jet penetration distance was measured to be 50% greater for the supersonic case at a CT = 3.0. Experimental results were compared with CFD calculations of the sonic 4-jet configuration. Very good comparison was shown in the streamline patterns and jet mole fraction distributions. Using the validated CFD model, preliminary calculations showed that the drag coefficient for the 4-jet peripheral case was 3 times larger than that for the single centerline jet case at a CT of 0.5 and 6 times larger at a CT of 1.5, both with sonic exit conditions and the same total mass flow rate. The preservation of the vehicle drag was attributed to the normal bow shock between the peripheral jets which does not exist in the single centerline jet. The total axial force coefficient (sum of CT and CD) was calculated to be twice as large for the peripheral 4 sonic jets as for the single sonic centerline jet at a CT of 0.5 and 50% larger at a CT of 1.5. This result suggests that, for the same total mass flow rate and sonic exit Mach number, the propulsive deceleration performance of the peripheral 4-jet PD design will be considerably greater relative to the single centerline PD jet. This result is important for the design of PD jet decelerators for EDL for future HMMES missions.

Numerical Investigation of Multinozzle Propulsive Deceleration Jets for Mars Entry Aeroshells

The effects of peripheral propulsive decelerator jets on the deceleration performance of Mars entry aeroshells are examined using computational fluid dynamics. The study considers a 70xa0deg blunt-cone aeroshell with four peripheral jets in Mach 12 flow of iodine-seeded nitrogen gas. Sonic and supersonic peripheral decelerator jets are considered in this study. The results show that the peripheral jets increase the standoff distance and change the profile of the bow shock around the aeroshell. The results also show that decelerator jets obstruct the flow around the aeroshell, which creates a low-pressure region on the surface behind the jets. The level of obstruction increases with thrust, which expands the low-pressure region. As a result, the aerodynamic drag coefficient of the aeroshell is inversely proportional to the thrust. The jet Mach number, however, has a small effect on the deceleration performance, with a maximum difference of less than 2% in the axial force between sonic and supersonic peripher...

Aerodynamic Interactions of Reaction-Control-System Jets for Atmospheric Entry Aeroshells

The fluid interactions produced by a sonic reaction-control-system thruster are investigated using computational fluid dynamics. The study uses a scaled Mars Science Laboratory aeroshell at a 20xa0deg angle of attack in Mach 12 flow of I2-seeded N2 gas. The reaction-control-system jet is directed either parallel or transverse to the freestream flow to examine the effects of the thruster orientation. The results show that both the parallel and transverse reaction-control-system jets obstruct the flow around the aeroshell and impinge on the surface, increasing the overall pressure along the aftbody. As a result, the reaction-control-system jet decreases the drag, lift, and moment acting on the aeroshell, particularly at relatively large reaction-control-system thrust conditions. The results also indicate that the fluid interactions produced by the parallel and transverse jets affect the control effectiveness of the reaction control system. The performance of the parallel reaction-control-system thruster is cl...

Interactions of Single-Nozzle Supersonic Propulsive Deceleration Jets on Mars Entry Aeroshells

As themass and landing site altitude of futureMars entry systems increase, the size requirements for conventional aerodynamic decelerators are becoming unfeasible. One option is propulsive decelerator jets. The use of propulsive decelerator jets, however, involves complex flow interactions that are still not well understood. This paper describes numerical and experimental techniques currently used to investigate these interactions. The paper also presents computational results for single-nozzle sonic propulsive decelerator jets. The numerical simulations use a scaled Mars Science Laboratory aeroshell in Mach 12 laminar flow of I2-seeded N2 gas. The results show that flowfield features, such as the bow andpropulsive decelerator jet shocks, are affected by the thrust coefficient of the propulsive decelerator nozzle. These effects also extend to the surface and aerodynamic properties of the aeroshell. As the thrust coefficient increases, the pressure and shear stress approach roughly constant values over most of the aeroshell surface, and the drag coefficient decreases and approaches a constant value equal to approximately 8% of the value for the propulsive decelerator jet-off case. Finally, comparisons between the numerical results and experimental data show good agreement in the bow shock profile and standoff distance, as well as the aerodynamic properties of the aeroshell.

Propulsion deceleration studies using Planar Laser-Induced Iodine Fluorescence and computational fluid dynamics

Future high-mass spacecraft entering the thin Martian atmosphere will require additional means of deceleration prior to deploying supersonic parachutes. Propulsive deceleration is one technology that is being considered. The interaction of the spacecraft aerodynamics with the propulsion deceleration (PD) jets has been shown to cause a decrease in drag coefficient with increasing thrust coefficient, which is not desirable for deceleration. Planar LaserInduced Iodine Fluorescence (PLIIF) images showed a lifting of the vehicle bow shock away from the aeroshell. Flowfield calculations performed using a CFD code showed that this lifting was responsible for the decrease in drag with increasing PD jet thrust. With 4 PD jets located midway between the aeroshell centerline and shoulder, PLIIF images showed that the vehicle bow shock is maintained between the jets as the thrust coefficient is increased. CFD calculations established that this bow shock was responsible for greater drag preservation with the peripheral jets. The peripheral jet drag coefficient was 4 times larger than the single jet value at a thrust coefficient of 2.0. The calculations also showed low pressure wakes located radially behind the peripheral jets which are responsible for the decrease in drag coefficient with increasing thrust coefficient and that high pressure is maintained between the jets. These results suggest that using a few peripheral PD jets located near the aeroshell shoulder would provide the greatest amount of drag preservation when using propulsive deceleration.

Investigations of Peripheral Propulsive Deceleration Jets on a Mars Science Laboratory Aeroshell

The objective to send more massive landed missions to the surface of Mars necessitates further research and development for ways to adequately decelerate the lander, such as propulsive deceleration. Experimental measurements using planar laser-induced iodine fluorescence provide qualitative visualizations and quantitative propulsive decelerator jet mole fraction measurements over a 0.22% scaled Mars Science Laboratory aeroshell. Peripheral (off-centerline) sonic and supersonic propulsive decelerator jet models, with jet exit velocities of Mach 1.0 and 2.66, were studied in Mach 12 flow and compared with numerical results obtained using computational fluid dynamics. Experimental visualizations were obtained for various thrust coefficients ranging from 0.5 to 3.0 in increments of 0.5. Experimental results indicate that, for both sonic and supersonic jets, the bow shock is preserved between the peripheral jets and, as thrust coefficient increases, the bow shock is pushed farther from the aeroshell forebody, ...