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International audience; A bi-frequency open-loop control strategy aiming to combine both high- and low-frequency forcing effects is used to experimentally reduce the drag of a simplified car model at a slight yaw angle of 5∘. The unforced mean wake features a lateral asymmetry which induces a low base pressure footprint close to the leeward side and increases drag compared to the aligned model. Forcing is performed with pulsed jets along the windward trailing edge. High-frequency forcing acts as a time-invariant flap. The fluidic flap effect deviates the windward shear layer towards the leeward side and reduces the wake bluffness, but the lateral asymmetry of the near wake is still observed. The drag reduction related to this high-frequency forcing is about 6% with a high actuation efficiency. A modulation of the high-frequency forcing with a low-frequency component is then introduced in order to modify the mass and momentum exchange in the separating shear layer at the windward trailing edge. We find that the modulated forcing provides the ability to manipulate the mean wake orientation while maintaining the fluidic flap effect. Among all wake orientations, those reducing drag are the ones having a mean symmetric wake. The bi-frequency control strategy leads to a maximum drag reduction of 7% for the best choice of frequencies. Importantly, the bi-frequency control is more efficient than the single high-frequency forcing, the actuator requiring only half the actuation energy and presenting an actuation efficiency multiplied by 3. Finally, the physical mechanisms related to drag reduction are carefully analyzed. In particular, we show that the wake symmetrization reduces the global production of turbulent kinetic energy in the shear layers. These results open up opportunities for closed-loop control of wake asymmetries.

International audience; The present manuscript deals with experimental investigations on thermal effects of air leakage zones at the boundaries of the vehicle hood. Measurements are carried out on a Peugeot 207 (Front Wheel Drive) in wind tunnel. The front wheels are activated by the car's engine and rolling on controlling rollers built in the wind tunnel. In parallel, the wind velocity is well controlled in order to simulate real conditions of driving. The underhood compartment is equipped with 80 thermocouples distributed on different components. Three operating conditions are studied according to the engine's rpm, to the wind and wheels velocities. The leakage zones are purposely clogged with five different configurations. The effect of the leakage zones has shown significant impact on the temperature field and has been physically analyzed.

The thermal performance of automotive heat exchangers is greatly affected by the relationship that binds the nonuniformities in flow velocity and the distribution of upstream temperatures. Consequently, an in-house two-dimensional code is established to evaluate the thermal performance based on known parameters, namely, distribution of upstream velocity of an air-liquid heat exchanger, the flow rate of heat exchanger liquid, and the inlet air and liquid temperatures. A parametric research study is then performed to confirm the relation between the thermal performance of the heat exchanger and these different parameters. It was observed that nonuniformities in air velocity and water flow distributions decrease the thermal performance of a heat exchanger by up to 33 and 42%, respectively.

International audience

The thermal soak phase of a vehicle results from driving the vehicle at high load followed by shutting off the engine. The present work deals with the analysis and modeling of the thermal soak phase of a vehicle through temperature and heat flux measurements. Measurements are carried out on a passenger vehicle in wind tunnel S4 of Saint-Cyr-France. The underhood is instrumented by alsmot 120 surface and air thermocouples and 20 fluxmeters. Measurements are performed for three thermal functioning conditions, with the engine in operation and the front wheels positioned on the test facility with power-absorption controlled rollers. It was found that in thermal soak the temperature of certain components can increase by almost 80A degrees C (pre-catalyst) and that of air zones by alsmot 40A degrees C (crawl area). These components correspond to areas that heat up after stopping the engine for 3 to 24 minutes, depending on their position in the underhood and on the thermal operating point considered.

International audience; We investigate experimentally a novel model-free controlstrategy, called Machine Learning Control (MLC), foraerodynamic drag reduction of a 3D bluff body. Fluidicactuation is applied at the blunt trailing edge of the bodycombined with a curved deflection surface. The impact ofactuation on the flow is monitored with base pressure sensors. The applied model-free control strategy detects andexploits nonlinear actuation mechanisms in an unsupervised manner with the aim of minimizing the drag. Keyenabler is linear genetic programming as simple and efficient framework for systems with multiple inputs (actuators) and multiple outputs (sensors). The ansatz of control laws include periodic forcing, multi-frequency forcing and sensor-based feedback control. Approximately33% base pressure recovery is achieved by the optimalcontrol law for a turbulent flow at Re_H ≈ 3 × 10 5 basedon body height.

International audience; Experimental and numerical analyzes were performed to investigate the aerodynamic performances of a realistic vehicle with a different afterbody rounding. This afterbody rounding resulted in a reduction to drag and lift at a yaw angle of zero, while the crosswind performances were degraded. Rounding the side pillars generated moderate changes to the drag and also caused important lift reductions. A minor effect on the drag force was found to result from the opposite drag effects on the slanted and vertical surfaces. The vorticity distribution in the near wake was also analyzed to understand the flow field modifications due to the afterbody rounding. Crosswind sensitivity was investigated to complete the analysis of the aerodynamic performances of the rounded edges models. Additional tests were conducted with geometry modifications as spoilers and underbody diffusers.

International audience; Experimental analyzes were performed to understand the drag evolution and the flow field modifications resulting from afterbody rounding on the Ahmed body, a simplified vehicle model with 25 degrees rear slant. Curvature effects were investigated using balance measurements, flow visualizations, wall pressure, and particle image velocimetry measurements. The rear end of the original well-known Ahmed body has sharp connections between the roof and the rear window as well as squared rear pillars. Similarly to previous studies, rounding the roof/backlight intersection was shown to reduce drag up to 16 %. Surprisingly, additional rear curvature associated with side pillar rounding did not further modify the drag. However, the zero net effect was found to result from opposite drag effects on the slanted and vertical surfaces and to hide strong local modifications on the flow field. The tridimensional organization and vorticity transport in the near wake were analyzed and connected to the observed local increase in the pressure drag on the base. Finally, these results were shown to be generic for a realistic rounded-end car shape.

Fans are often tested without downstream blockage and, thus, the performance is considerably different when the fan is mounted in a vehicle as part of a cooling system and where high blockage effect is present downstream. The aim of the present work is to analyze by laser Doppler velocimetry LDV measurements the topology of the flow induced by a fan incorporated in a simplified underhood model reproducing engine blockage and to study the blockage effect of the engine positioning on the flow induced by the fan. The distance between the fan and the engine block affects the mean flow axial velocity U. The vertical velocity component W is greatly influenced by the variation of the distance between the fan and the engine block, both in magnitude and topology.

Parametric numerical analysis that explores the relation between the non-uniformity of air temperature distribution upstream of a heat exchanger and its thermal performance is performed. The obtained numerical results are employed toward the optimization of water-air heat exchanger thermal performance. Furthermore, the numerical results lay out the foundation to develop an innovative control approach for monitoring the airflow upstream of a cross-flow water-air heat exchanger that lead to the optimization of its thermal performance and energy consumption. Consequently, an in-house computational code is established to evaluate the aforementioned thermal performance based on known parameters; namely, distribution of upstream velocity and temperature of an air-liquid heat exchanger, the flow rate of heat exchanger liquid, in addition to the inlet liquid temperature. It was observed that non-uniformities in air temperature can, depending on the configuration, increase or decrease the thermal performance of a heat exchanger up to 5%. Additionally, controlling air temperature non-uniformities, the fuel consumption and carbon dioxide emission can be reduced by up to 0.97 kg (1.34 L) and 3.17 kg respectively for a vehicle running three hours per day. (C) 2016 Elsevier Ltd. All rights reserved.

We report here experimental results focused on the optimization of vehicle underhood cooling module. These results constitute the basis for a new approach of controlling the cooling module positioning according to the engine energy requirements. Measurements are carried out on a simplified vehicle body designed based on the real vehicle front block. We report here velocity and temperature measurements by Particle Image Velocimetry (Ply), by Laser Doppler Velocimetry (LDV) and by thermocouples. The underhood of the simplified body is instrumented by 59 surface and fluid thermocouples. Measurements are carried out for conditions simulating both the slowdown and the thermal soak phases with the fan in operation. Different fan rotational speeds, radiator water flow and underhood geometries have been experimented. The ultimate aim is to apply the new control approach to a real vehicle so as to reduce the energy delivered to the pump and compressor and therefore to reduce the vehicle fuel consumption. (C) 2011 Elsevier Ltd. All rights reserved.

The present paper reports a numerical investigation of spatial optimization of heat-exchanger by acting on its positioning in the vehicle's cooling module. This analysis also elucidates how to act on the different parameters influencing heat-exchanger performance in order to optimize their functioning. A two-dimensional computation code permits optimizing the performance of the cooling module by positioning different heat exchangers, in both the driving and stop phases of the vehicle. The ultimate aim is to apply new control approaches to real vehicles so as to reduce pump and compressor energy consumption and thus fuel consumption. Compared to a reference "in-series" configuration of the cooling module HXs (in which the different HXs are superposed in the airflow direction), an "in-parallel" configuration (in which the different HX surfaces are in a row with respect to the air flow direction) increases the thermal power of the HXs by 4.4% and decreases the pressure losses by 0.9%. (C) 2011 Elsevier Ltd. All rights reserved.

Using the basic equations for modeling heat transfer through heat exchangers, an analytical approach is developed to determining the thermal performance of cross-flow air-cooled heat exchangers as a function of the flow statistics of the upstream cooling air. A two-dimensional computational code is also developed to calculate heat-exchanger performance in relation to the airflow topology upstream of the heat exchanger induced by its integration in complex environments such as the car underhood compartment. The analytical and numerical results show satisfactory agreement: the mean relative error in heat exchanger thermal performance determined by the numerical computation and the analytical approach is about 0.5%. (C) 2010 Elsevier Ltd. All rights reserved.

It has been shown by the authors that car inclination influences the temperatures of different underhood components. Here these effects are analyzed by heat-flux measurements. The results of underhood temperature and heat-flux measurements carried out on a passenger vehicle in wind-tunnel S4 of Saint-Cyr l'Ecole are presented. The underhood compartment of the vehicle is instrumented with 40 surface and air thermocouples and 20 flux meters of normal gradient. Experiments are performed with a specific technique for separate measurement of convective and radiative heat fluxes. Three car position configurations are tested: flat, uphill, and downhill positions. Measurements are made for three different thermal functioning modes. Fluxmetric analysis based on overall heat flux as well as on separate convective and radiative heat fluxes is reported here in order to establish the effects and variation tendencies of car inclination on the temperature-heat flux pair. For most of the tested positions in the underhood top region, the car inclination improves convective heat transfer and penalizes radiative heat transfer. The reduction in radiative heat transfer dominates the convective heat-transfer improvement, resulting in augmentation of the overall heat flux as well as the temperature.

The leakage areas of the engine compartment are located essentially at the junctions between the hood and the front end, the sides, the lights, and the windshield. The present study concerns the impact of these leakage zones on the engine compartment temperatures. The study synthesizes thermal measurements carried out on a real vehicle in the wind tunnel S4 of Saint-Cyr l’Ecole France. The engine compartment is instrumented with 80 surface and air thermocouples. Measurements are carried out for three different thermal functioning points with the front wheels of the vehicle positioned on a dynamometer and driven by the engine of the car. Five configurations of leakages closing are tested.

Convective and radiative heat fluxes enter simultaneously into most thermal engineering applications, especially in the vehicle underhood. However, separate measurements of these fluxes are needed for understanding and analyzing underhood aerothermal phenomena. In this context, a new experimental technique has been proposed (Khaled et al 2010 Meas. Sci. Technol. 21 025903) that allows the simultaneous measurement of convective and radiative heat fluxes. The technique uses a pair of fluxmeters with different radiative properties: the two fluxmeters measure the same convective flux but different radiative fluxes proportional to the fluxmeters' emissivities. This permits the separate calculation of the convective and radiative fluxes. This paper presents a sensitivity and applicability analysis of the new technique, taking into account the effects of a number of parameters such as emissivities, the precision of emissivity estimation and the difference in convective heat fluxes due to fluxmeter position. Also, new applications of this novel technique are proposed as an alternative when the initial version becomes inaccurate.

This paper presents an experimental investigation of the underhood thermal behaviors during vehicle thermal soak (when the vehicle stops after a large thermal load) by temperature measurement and separate measurements of convective and radiative heat fluxes. Measurements are carried out on a passenger vehicle in wind tunnel S4 of Saint-Cyr-France. The underhood is instrumented by almost 120 surface and air thermocouples and 20 fluxmeters. Measurements are performed for three thermal functioning conditions, with the engine in operation and the front wheels positioned on the test facility with power-absorption controlled rollers. It was found that in thermal soak the temperature of certain components can increase by almost 80°C (pre-catalyst screen) and that of air zones by almost 40°C (crawl area).Copyright © 2013 by ASME

Air leakage from the engine compartment of a vehicle comes mainly from the junctions of the vehicle hood and the front end grill, the vehicle wings, the optical and the windshield. The present paper studies the thermal impact of these air leakage zones on the components of the vehicle engine compartment through temperature and heat-flux measurements. The front wheels of the test vehicle are positioned on a dynamometer and driven by the vehicle engine. The engine compartment is instrumented with almost 100 surface and air thermocouples and 20 fluxmeters of normal gradients. Measurements were made for three different thermal operating points. Five leak-sealing configurations are studied.

This paper concentrates on the assessment of automobiles aerothermal management; namely, the consequence of the architectural arrangements of electrical and mechanical components on the aerothermal behavior in the underhood compartment. Consequently, it is natural to review the architectural arrangements of underhood components implemented by automotive companies such as Renault, Peugeot, Audi, BMW, Mercedes, Volvo, General Motors, Jaguar, Land Rover, Porsche, Nissan, Chrysler, Ford, Hyundai, Kia, and Toyota. Moreover, this study will evaluate the qualitative impact of each individual component on the aerothermal environment of the underhood. Furthermore, the study is determined to examine explicitly the components architectural arrangements' of underhood compartments and present simplified models of the compartments so that they can serve as aerothermal baseline models in the early stages of design. Hence, the different components in the underhand compartment are classified with respect to aerothermal orders of impact. Followed, two geometrical models, simple and advanced, are developed based on the impact orders. These models serve for future aerothermal studies (analytical, numerical and experimental). Finally, a simplified vehicle model is designed and implemented as underhood compartment model. The structurally simplified model is already utilized in experiments and can be used afterward in both numerical and experimental analyses. (C) 2014 Elsevier Ltd. All rights reserved.

In the present work, a two-dimensional code is developed to calculate the heat-exchanger thermal performance in relation to the airflow topology upstream of the heat exchanger induced by its integration in complex environments such as the car underhood compartment. It was shown that the non-uniformity in the upstream velocity distribution decreases the thermal performance of the heat exchanger.

This paper presents a numerical analysis focused on the relation between non-uniformities in flow velocity and temperature distributions upstream of heat exchangers and their thermal performance. For this purpose, a two-dimensional computation code is developed to compute thermal performance, knowing the air flow velocity distribution upstream of an air-liquid heat exchanger, the heat exchanger liquid flow rate and the air and liquid inlet temperatures. A parametric analysis is then presented of the relation between the thermal performance of the heat exchanger and the different parameters above. It is found that non-uniformities in air velocity and water flow distributions can decrease the thermal performance of a heat exchanger from 33 to 42%. However, non-uniformity in the air temperature distribution can increase thermal performance by up to 5%.Copyright © 2013 by ASME

This work reports on experiments carried out on a real passenger vehicle in a large wind tunnel to investigate the effects of car inclination on underhood cooling. The vehicle’s underhood is instrumented by thermocouples that measure the temperatures of many underhood components during different car functioning modes. Measurements are carried out for three thermal functioning points at car speeds 90, 110 and 130 km/h. In these experiments the engine was in operation and the front wheels positioned on the test facility with power-absorption-controlled rollers. Three car inclinations are investigated: flat, uphill and downhill. The results show that car inclination, even if very small, can have significant effects on underhood cooling and must be taken into consideration in numerical simulations and controlled in experimental tests. It was shown that down-hill and up-hill inclinations increase temperatures of components, air zones and engine parameters in the underhood, with higher effect for the down-hill inclination. Temperature increases in constant-speed driving phase are higher than in thermal soak phase.

The aerodynamic torsor of a vehicle is among the most crucial parameters in new car development. This torsor has been decreased over the years by more than 33%, but beyond that further improvement has become difficult and challenging for car manufacturers. In this context, the present paper focuses on a parametric analysis of the trends in the aerodynamic forces. We report here aerodynamic force measurements carried out on a simplified vehicle model. Tests were performed in wind tunnel S4 of Saint-Cyr l'Ecole for different airflow configurations in order to isolate the parameters that affect the aerodynamic torsor and to confirm others previously suspected. The simplified model has flat and flexible air inlets and several types of air outlet, and includes in its body a real cooling system and a simplified engine block that can move in the longitudinal and lateral directions. The results of this research, which can be applied to any new car design, show configurations in which the overall drag coefficient can be decreased by 2%, the aerodynamic cooling drag coefficient by more than 50% and the lift coefficient by 5%. Finally, new designs for aerodynamic drag reduction, based on the combined effects of the different parameters investigated, are proposed. (C) 2012 Elsevier Ltd. All rights reserved.

The present paper reports an experimental study of the aerothermal phenomena in the vehicle underhood compartment as investigated by measuring temperature, convective heat flux, and radiative heat flux. Measurements are carried out on a passenger vehicle in wind tunnel S4 of Saint-Cyr-France. The underhood space is instrumented by 120 surface and air thermocouples and 20 fluxmeters. Measurements are performed for three thermal functioning conditions while the engine is in operation and the front wheels are positioned on the test facility with power-absorption-controlled rollers. In the thermal analysis, particular attention is given to measuring absorbed convective heat fluxes at component surfaces. It is shown that, in some components, the outside air entering the engine compartment (for cooling certain components) can in fact heat other components. This problem arises from the underhood architecture, specifically the positioning of some components downstream of warmer components in the same airflow. Optimized thermal management suggests placing these components further upstream or isolating them from the hot stream by deflectors. Given style constraints, however, the use of air deflectors is more suitable than underhood architectural changes. Much of the present paper is devoted to heat flux analysis of the specific thermal behaviours in the underhood compartment (especially the absorption of convective heat fluxes) and to a description of a new control approach exploiting air deflectors to optimize underhood aerothermal management. (C) 2010 Elsevier Ltd. All rights reserved.

The present paper exposes the study of the cooling system circulation effect on the external aerodynamic forces. We report here aerodynamic force measurements carried out on a simplified vehicle model in wind tunnel. Tests are performed for different airflow configurations in order to detect the parameters that can affect the aerodynamic torsor and to confirm others previously suspected, especially the air inlets localization, the air outlet distributions and the underhood geometry. The simplified model has flat and flexible air inlets and several types of air outlet, and includes in its body a real cooling system and a simplified engine block that can move in the longitudinal and lateral directions. The results of this research are generic and can be applied to any new car design. Results show configurations in which, with respect to the most commonly adopted underhood geometries, the overall drag coefficient can be decreased by 2%, the aerodynamic cooling drag coefficient by more than 50% and the lift coefficient by 5%. Finally, new designs of aerodynamic drag reduction, based on the combined effects of the different investigated parameters, are proposed.

In this work heat transfer and temperature behavior of complex flows encountered in the vehicle underhood compartment is experimentally studied and described with simple models. Underhood thermal measurements made on a passenger vehicle in a large-scale wind tunnel are reported here. The underhood is instrumented by 80 surface and air thermocouples and 20 fluxmeters. Measurements are carried out at three thermal functioning points, in all of which the engine is in operation and the front wheels are positioned on the test facility with power-absorption-controlled rollers. Models are proposed to predict the maximum temperatures and time constants of the underhood components as functions of the car speed and car engine power. The relative errors of the models are 3.6% and 3.7%, respectively. The maximum temperature and the time constant are crucial in the design and optimization of the underhood aerothermal management system. The results obtained in the present work also provide a large database for validation of numerical codes dealing with underhood cooling management.

It is now well established that car inclination influences component temperatures in the car underhood compartment [1, 2]. This study presents an analysis of these effects by measurement of the heat flux that enters or leaves the underhood components. We report underhood thermal measurements carried out in wind-tunnel S4 of Saint-Cyr l’Ecole on a passenger vehicle. The underhood compartment is instrumented with 40 surface and air thermocouples and 20 fluxmeters of normal gradients. Three configurations of car positions are investigated: the flat, the up-hill and the down-hill inclinations. Measurements are carried out for three different car thermal functioning points.Copyright © 2010 by ASME

An experimental analysis of the aerothermal phenomena in the vehicle underhood is given using temperature measurements and separate measurements of convective and radiative heat fluxes. The vehicle underhood used for these measurements is instrumented by 120 surface and air thermocouples and 20 fluxmeters. Measurements are carried out on a passenger vehicle in wind tunnel S4 of Saint-Cyr-France for three thermal functioning conditions. In particular, it is shown for some components that outside air entering the engine compartment (for cooling the different components by convection) can in fact heat other components. This problem results from the underhood architecture, specifically the positioning of some components downstream of warmer components in the same airflow. To avoid this undesired situation, an optimized thermal management procedure is proposed that uses static and dynamic air deflectors during the constant-speed driving (rooting) phase of a vehicle. Much of the present paper is devoted to fluxmetric analysis of underhood thermal behavior (especially the absorption of convective heat flux); we also describe a new control procedure for implementing air deflectors in the actual car underhood.Copyright © 2010 by ASME

Here numerical analysis is focused on optimizing the vehicle heat exchanger by varying the geometry in which it is integrated in the vehicle’s cooling system. This analysis also elucidates how one can affect the different parameters that influence heat exchanger performance in order to optimize their functioning, in relation to the geometry in which they are integrated. The two-dimensional computational code developed permits optimizing the performance of the cooling module by positioning different heat exchangers, in both driving and stop phases of the vehicle. The ultimate aim is to develop new approaches to controlling heat exchanger positions in a real vehicle cooling system.

Aerodynamic cooling drag, caused by car underhood cooling, can be reduced by better underhood aerothermal management. This study addresses the aerothermal phenomena encountered in the vehicle underhood compartment by physical analysis of the heat transfer modes in complex internal flows. We report here underhood heat flux and temperature measurements on a vehicle in wind tunnel S4 of Saint-Cyr-France using a new experimental method. The underhood is instrumented by 40 surface and air thermocouples and 20 fluxmeters. Measurements are carried out for three thermal functioning points: the engine in operation and the front wheels positioned on the test facility with power-absorption-controlled rollers. The ultimate aim is to reengineer the underhood architecture so as to reduce the cooling air flow rate in the underhood component and hence the aerothermal cooling drag. (C) 2009 Elsevier Ltd. All rights reserved.

The study presented here concerns the impact of car inclination on the temperatures in the vehicle underhood compartment. We report here underhood thermal measurements carried out on a vehicle in wind tunnel S4 of Saint-Cyr, France. The underhood is instrumented by 80 surface and air thermocouples. Measurements are carried out for three different thermal charges (thermal functioning points). During tests, the engine is in operation, and the front wheels positioned on the test facility equipped with rollers, permitting the wheel power and rotational speed control. Three car inclinations are tested.

International audience; We experimentally investigate the propagation of chemical fronts in steady laminar cellular flows at large Péclet numbers and large Damköhler numbers. Fronts are generated in an aqueous solution by an autocatalytic oxydoreduction reaction. They propagate in a channel in which a chain of counter-rotative parallel vortices is induced by electroconvection. We first accurately determine the form, the dynamics and the mean velocity of these fronts in the whole Hele-Shaw regime of the flow. We then address the modeling of the evolution of their mean velocity with the flow amplitude. The structure of the front wakes yields us to reject an effective reaction-diffusion wave as a relevant model for large-scale front propagation. On the other hand, analysis of the role of front heads brings us to introduce a kinematic model at the vortex scale for uncovering the front dynamics. This model addresses the propagation of the front leading point in a chain of vortices whose field is modeled by a two-dimensional solid rotation complemented by a boundary layer. Interestingly, it sensitively relies on the effective trajectory followed by the front leading point. To account for this, a competition is worked out among a one-parameter family of potential trajectories. The actual trajectory is then selected as the fastest one with quite a good agreement with measurements and observations. In particular, the measured effective front velocities are well recovered from the model, including their intrinsic dependence on the boundary layer width. Accordingly, effective front propagation in a laminar steadily stirred medium is thus understood from an optimization principle similar to the Fermat principle of ray propagation in heterogeneous media.

In this paper, we present the first characterization of new pulsed microjets. The specificity of these new actuators is their large nozzle for MEMS device: the total exit cross-section on a single actuators can reach up to 3×3.28 mm2 ⋍ 10 mm2. Two different geometries are presented: one with a single slot and one with three slots on a single MEMS device. We measure the jet velocities as a function of the inlet pressure. Maximum jet velocity can reach up to 28 m/s with a pulsation frequency around 100 Hz. Other phenomena are discussed, like the deviation of the jet axis from the vertical and the wrong evaluation of the jet velocity close to the nozzle.We finally apply the three slots actuators to a backward-facing step flow and show a small reduction of the recirculation length when the pulsation frequency is equal to the shear layer frequency.

The study presented here concerns the impact of car inclination on the temperatures in the vehicle underhood compartment. We report here underhood thermal measurements carried out on a vehicle in wind tunnel S4 of Saint-Cyr. The underhood is instrumented by 80 surface and air thermocouples. Measurements are carried out for three thermal functioning points: the engine in operation and the front wheels positioned on the test facility with power-absorption-controlled rollers. Three car inclinations are tested.

International audience

We investigate open- and closed-loop active control for aerodynamic drag reduction of a car model. Turbulent flow around a blunt-edged Ahmed body is examined at $Re_{H}\approx3\times10^{5}$ based on body height. The actuation is performed with pulsed jets at all trailing edges combined with a Coanda deflection surface. The flow is monitored with pressure sensors distributed at the rear side. We apply a model-free control strategy building on Dracopoulos & Kent (Neural Comput. & Applic., vol. 6, 1997, pp. 214-228) and Gautier et al. (J. Fluid Mech., vol. 770, 2015, pp. 442-457). The optimized control laws comprise periodic forcing, multi-frequency forcing and sensor-based feedback including also time-history information feedback and combination thereof. Key enabler is linear genetic programming as simple and efficient framework for multiple inputs (actuators) and multiple outputs (sensors). The proposed linear genetic programming control can select the best open- or closed-loop control in an unsupervised manner. Approximately 33% base pressure recovery associated with 22% drag reduction is achieved in all considered classes of control laws. Intriguingly, the feedback actuation emulates periodic high-frequency forcing by selecting one pressure sensor in the optimal control law. Our control strategy is, in principle, applicable to all multiple actuators and sensors experiments., 39 pages, 23 figures

International audience; We investigate experimentally a novel model-free in-time control strategy, calledMachine Learning Control (MLC), for aerodynamic drag reduction of a car model. Fluidicactuation is applied at the trailing edge of a blunt-edged Ahmed body combined with a curveddeflection surface. The impact of actuation on the flow is monitored with base pressure sensors.Based on the idea of genetic programming, the applied model-free control strategy detects andexploits nonlinear actuation mechanisms in an unsupervised manner with the aim of minimizingthe drag. Key enabler is linear genetic programming as simple and efficient framework formultiple inputs (actuators) and multiple outputs (sensors). The optimized control laws compriseperiodic forcing, multi-frequency forcing and sensor-based feedback control. Approximately 33%base pressure recovery associated with 22% drag reduction is achieved by the optimal controllaw for a turbulent flow at Re H ≈ 3 × 10 5 based on body height.