The Aerodynamics of Heavy Vehicles III

Slipstream is the flow that a train pulls along due to the viscosity of the fluid. In real life applications, the effect of the slipstream flow is a safety concern for people on platform, trackside workers and objects on platforms such as baggage carts and pushchairs. The most important region for slipstream of high-speed passanger trains is the near wake, in which the flow is fully turbulent with a broad range of length and time scales. In this work, the flow around the Aerodynamic Train Model (ATM) is simulated using Detached Eddy Simulation (DES) to model the turbulence. Different grids are used in order to prove grid converged results. In order to compare with the results of experimental work performed at DLR on the ATM, where a trip wire was attached to the model, it turned out to be necessary to model this wire to have comparable results. An attempt to model the effect of the trip wire via volume forces improved the results but we were not successful at reproducing the full velocity profiles. The flow is analyzed by computing the POD and Koopman modes. The structures in the flow are found to be associated with two counter rotating vortices. A strong connection between pairs of modes is found, which is related to the propagation of flow structures for the POD modes. Koopman modes and POD modes are similar in the spatial structure and similarities in frequencies of the time evolution of the structures are also found.

Results obtained from two component Particle Image Velocimetry (PIV) measurements on three different 1:50 generic high-speed train configurations hauled through a water towing tank over a smooth (Plexiglas) and a rough (grinding belt) ground at a speed of 4 m/s are presented. Principally, the three different generic high-speed train configurations are based on the same model (front car, two cars and tail car). The smooth generic high-speed train configuration (smooth GHSTC) reflects no bogies and covers the bogie cut outs and inter car gaps, the rough generic high-speed train configuration (rough GHSTC) is obtained by removing the bogies and leave the bogie cut outs and inter car gaps open and for the generic high-speed train configuration (GHSTC) the bogies are not removed but the inter car gaps are left open. A PIV set-up was chosen that the light sheet defines a vertical plane (XZ) between the ground and the train in the symmetry line of the train. Comparing the PIV results obtained for the GHSTC with full scale measurements, it was found that the same flow structures develop in the vicinity of the head and the tail of the train. But, the measured underfloor U-velocity of the downscaled model measurements did not reach the same value as those measured for the full scale high-speed train. The reason which is ascribed to the better aerodynamic underframe of the train model in the downscaled model measurements. The flow field underneath the GHSTC was fully developed at the beginning of the second car, in agreement to the full scale measurements. For the three train configurations three different flow fields underneath the train were obtained. The lowest velocities were found for the smooth GHSTC and the highest for the rough GHSTC. Further, the ground roughness changed the flow fields underneath the different train configurations.

A three-part study was conducted to determine the effectiveness of retrofit aerodynamic drag reducing devices on the fuel consumption and economics of open-top, bulk commodity, gondola and hopper rail cars in unit train service. Specific applications included trains transporting coal from mines to power plants. During the first part of the study wind tunnel testing and computational fluid dynamics were combined with an extensive literature search to rank the drag reducing effectiveness of a variety of devices including covers, internal baffles, end treatments, gap fillers, car side geometry, and underbody modifications. During the second portion of the study, three approaches were utilized to determine fuel savings associated with each aerodynamic retrofit device. These included two classical methods and a newly-developed train energy model. Results were validated using fuel consumption data provided by a U.S. Class I railroad. During the third portion of the study, an economic analysis of the candidate devices was completed which included the following parameters: weights of the retrofit devices, manufacturing and installation costs, drag reduction effectiveness, and projected return on investment. The study predicted round trip fuel savings, due to the addition of aerodynamic modifications to open-top rail cars in unit-train service, ranging from 2.7 to 19.9 % and return on investment durations as short as 2 years, depending upon the type of device, route, and car utilization. It was shown that economic viability of car modifications depends only partly on aerodynamic performance. Some of the modifications exhibiting high levels of drag reduction were eliminated from additional consideration due to high associated costs and negative impact on payload capacity.

In high-speed rail tunnels and heavy duty underground systems, aerodynamic issues have a substantial impact on the consumption of energy and resources. Together with the interrelated thermal conditions and the tunnel ventilation, various parameters of tunnel and vehicle design affect the resulting life-cycle costs and consequently the sustainability of these systems. For example, the power demand of metro systems is determined by the rolling stock features, the civil layout of tunnels and stations as well as by the way of operating the mechanical and electrical systems, including tunnel ventilation. Costs for traction power are influenced by vehicle design but equally by the choice of cross-sections and arrangement of shafts in the tunnel. Ventilation and cooling costs are caused by on-board systems of trains as well as by the equipment in tunnels and in stations. Thus, aero-thermal features of both, rolling stock and civil construction should be optimized together. During the design process, the above topics are commonly addressed separately. An overall system optimization covering for example rolling stock, civil design, track layout, tunnel ventilation and station ventilation is often missing. Awareness of rolling stock and infrastructure designers of the individual impact of the various factors affecting the energy demand of underground systems could be improved by more data for decision making. This paper aims at triggering more profound research work for a better understanding of the impact of the various design parameters on tunnel aerodynamics and the closely linked ventilation and cooling. Life-cycle costs would be reduced and a sustainable design shall be promoted.

Cross wind stability of the TSI HST reference vehicle ICE3 is numerically investigated for the six meter high embankment configuration. The focus of this numerical study is to investigate the sensitivity of the results on the embankment geometry and the position of the train on the embankment. This study is relevant as TSI HST does not explicitly specify the embankment configuration in the wind tunnel.

The correct definition of the crosswind aerodynamic forces on a high speed train is important to judge the safety of the rolling stock. Different conditions in terms of scenario (DTBR, EMBK and presence of wind barriers) and in terms of train motion are compared in the paper considering the aerodynamic forces and moments that mostly contribute to the overturning risk of the train while it is running under crosswind. The results of CFD simulations are compared and validated with experimental wind tunnel tests. The numerical model allows to make a comparison between the aerodynamic forces computed on the train for different angles of incidence, simulating a still model and a moving train model. The still model reproduces what is tested in the wind tunnel, while the moving model simulates the real condition of a train running under crosswind. This work analyzes the aerodynamic behavior of a ETR-500 train under crosswind in different scenarios.

In this paper the aerodynamic forces and moments on a high-speed train in a cross wind were obtained both numerically and experimentally. The train was positioned at the top of a 2 m high embankment. Experimental data was obtained using the Monash wind tunnel for a 1:20 scale model. These measurements were made over a range of yaw angles spanning \(0^{\circ }\)–\(90^{\circ }\). The numerical computations were performed using the commercial code FLUENT. These computations focused on the structure of the flow field around the high-speed train at different yaw angles. The model was discretized using a hybrid grid, with a total cell count of \(1.02 \times 10^{7}\). The predictions show a good match for the calculated aerodynamic force and moment coefficients with experimental measurements. Aerodynamic forces were determined for two cases: with the train on either the windward or the leeward track on top of the embankment. The side force is found to be greater for the leeward case, while the lift force for the leeward case is less than that for the windward case.

In the design process of trains wind tunnel tests are indispensable in order to assess the cross-wind sensitivity. The aerodynamic forces and moments acting on the leading cars or trailer cars can be measured and aerodynamic coefficients determined. Usually the tests are carried out at low turbulence conditions (“smooth flow”). During recent wind tunnel tests on new high speed train models in the Hermann-Föttinger Institute Berlin undesired Reynolds number effects were observed. This paper describes an approach to reduce these effects by changing the turbulence conditions of the flow. Wind tunnel measurement on a high speed train model in scale 1:25 are carried out with different turbulence conditions: increased free stream turbulence and a tripped boundary layer on the model. The free stream turbulence level is varied from 0.5 to 8 % by using grids with different geometries up stream of the test section. The experiments showed that the Reynolds number dependency on the saftey relevant rolling moment can be well reduced by a simple rectangular grid installed in the contraction of the wind tunnel.

The paper presents the results of a research activity studying the possibility to evaluate the cross wind velocity acting on a running train though surface pressure measurements. The research exploits the know-how developed in the aerospace field on FADS (Flush Air Data sensing Systems) and performs a complete design of the system. In particular, the choice of the number and the position of pressure taps on the surface of the train leading car is optimized, in terms of measurement system sensitivity and robustness, using a neural network approach and wind tunnel test results. A calibration of the system is performed and validated using wind tunnel tests on a moving train model.

The compression wave generated when a high-speed train enters a tunnel at Mach numbers smaller than 0.4 can be described in good approximation by a linear theory of an inviscid fluid. The wave equation for the acoustic potential becomes the governing equation. It is solved by a three dimensional boundary element method in time domain which forces a vanishing normal component of the velocity at the tunnel wall. It is assumed that the elements are compact in time. This leads to a linear equation in which a special matrix-vector multiplication has to be evaluated for every time-step. The aim is to create a fast method which sets as few constraints on the geometry as possible but nevertheless gives an accurate description of the wave propagation. In a first step the elements are assumed to be rectangles and an infinitely thin cylindric tube of finite length is taken as the geometry of the tunnel. The train is modeled by a single moving mass source of monopole type. It defines a semi-infinite body whose shape slightly changes when entering the tunnel. The results of this simple model along with the comparison with analytical solutions and experimental data are shown and discussed.

The present study focuses on the analysis of the main aeroacoustic sound sources of a high speed train, measured in a wind tunnel. The experiments using a 1:25 Inter City Express 3 model were carried out in two different wind tunnels: The Aeroacoustic Wind tunnel (AWB) of the German Aerospace Center (DLR) in Brunswick and in the Cryogenic wind tunnel (DNW-KKK) of the DNW (German Dutch wind tunnels) in Cologne. The AWB is a Goettingen type wind tunnel with open test section which is surrounded by an anechoic chamber. The advantage of this facility is its low background noise level and its nearly anechoic test section. The maximum Reynolds number, based on the wind speed and the width of the train, achieved is 0.46 million. In order to obtain higher Reynolds numbers a second measurement campaign has been conducted in the cryogenic wind tunnel, using another array for cryogenic in-flow applications. The DNW-KKK enables higher Reynolds numbers up to 3.7 million by cooling down the fluid to 100 K. The DNW-KKK has a closed test section and the microphone array is mounted on a side wall inside the wind tunnel, and therefore the measurements are affected by the turbulent boundary layer. Drawback of this facility is that it is not optimized for aeroacoustic experiments and reflexions as well as the high background noise level can disturb the results. Differences of the two different experimental setups on the results and primarily, influence of the Reynolds number on the aeroacoustic of a high speed train will be discussed.

In recent years, the strong pressure from both customers and government bodies toward improvement of fuel consumption and reduction of pollution has made it necessary for the manufacturers of road vehicles to pursue increasingly innovative solutions and novel technologies toward this end. The average heavy truck customer’s sophisticated understanding of a vehicle’s total cost of ownership cause the Heavy Truck Market to be driven by objective measures of vehicle performance to a larger degree than is present in most other road vehicle markets. The fuel consumption of a heavy truck is among the largest contributors to the vehicle’s total cost of ownership. As such, the improvement of fuel consumption through reduction of aerodynamic drag is of particular interest to Heavy Truck Manufacturers and their customers. Today, the optimization of aerodynamics for commercial vehicles must not be restricted merely to the installation of devices on the roof of the cabin. Rather, the vehicle must be regarded as a complete system and optimized accordingly. That is to say that aerodynamic optimization today focuses on the entire vehicle rather than just the tractor unit. Aerodynamic optimization must be balanced against such considerations as styling, ergonomics and soiling. The interactions between these various considerations will be explained through the use of some different cases. For example, the subject of windshield rake angle as it relates to headroom and aerodynamics. In closing, an outlook regarding the future development of Aerodynamic commercial vehicles will be given.

Modern trucks have a reasonably optimised cab shape, and there exist several OEM and aftermarket devices for drag reduction for heavy trucks as well. To further reduce the aerodynamic drag major changes to the current layout of the vehicle are required, or the focus must be shifted from the cab and tractor trailer gap to other regions of the vehicle. The drag of the underbody, including wheel housings, wheels and engine compartment, represents a significant proportion of the aerodynamic drag and there has not been much investigation in this specific area on heavy trucks. To be able to reduce the fuel consumption and to fulfil the legislated emission standards for heavy trucks it is important to take all areas of the vehicle under consideration, and even though the individual improvements may be small, the total drag reduction will be substantial. In order to study the flow close to the vehicle underbody it is important to utilise the correct boundary conditions, that is, moving ground and rotating wheels. This work has focused on the flow in the front wheel housings. The flow field around the front wheels under the influence of ground simulation on a heavy truck of standard European configuration was investigated using numerical simulations. The in- and outflow to the wheel housing was located and the vortices originating from the front wheels were identified. This information was then used to identify which areas of the wheel housing having the greatest potential for aerodynamic improvements by changing the front wheel housing design. Furthermore, several wheel housing design parameters were defined, and their influence on the flow field and aerodynamic drag were investigated. Examples of these parameters are the shape of the wheel housing opening and implementation of wheel housing ventilation. It was found that there is potential for reducing the aerodynamic drag by applying these geometric changes to the wheel housing, and several of the configurations could be implemented on current production vehicles.

Full scale CFD simulations of the Generic Conventional Model (GCM), a simplified model of a Class 8 truck, were used to explore passive devices for improving the drag performance of the trailer base. Significant improvements over conventional straight base flaps were achieved using an Extended Bent (EB) flap that stays within the length limits imposed by US federal law. An additional boat tail device for the cab bogie base was also found to yield improvements in the base drag in that region. This device in combination with the EB flap leads to a wind-averaged drag reduction of 21 % over the non-modified GCM model. An under-trailer scoop to generate air for pressurizing the trailer base or for use in active flow control devices was found to add too much drag to be effective.

Due to increasing environmental constraintsit is crucial for the heavy duty transport sector to find solutions to stay sustainable in this aggressive and fast changing market. Improving aerodynamic quality, i.e. reducing drag, will contribute largely to the solution for this issue. With numerical analysis of a standard tractor semi-trailer combination a general overview of the flow has been obtained: a highly complex flow and large separated regions can be observed. Wind tunnel experiments with a 1:14 scaled truck model are performed to experimentally analyze the effect of aerodynamic aids to reduce the drag of the tractor with trailer. Aerodynamically shaped skirts improve the drag reductions more then 14 %. Mounting a boat tail reduces the drag with 12 %. Full-scale prototypes are built and road tests are conducted. The aerodynamic skirts, called SideWings showed an averaged fuel economy increase 1.6 l/100 km when tested on the circuit and the road. During one year four different boat tail configurations are tested. A fuel saving of 2 l/100 km for the 2 m tail is obtained.

Large-eddy simulations and full-scale investigations were carried out that aimed to reduce the aerodynamic drag and thus the fuel consumption of truck-trailers. The computational model is a relevant generic truck-trailer combination, and the full-scale is a corresponding Volvo prototype vehicle. Passive and active flow control (AFC) approaches were adopted in this work and applied at the rear end of the trailer. Flaps were mounted at an angle that induces separation, and synthetic jet actuators were placed close to the corner of the rear end and the flaps. The drag reduction obtained is in the order of \(30\,\%\). The flow was analyzed by comparing the phase-averaged and time-averaged flow field of the unforced and the forced cases. The full-scale prototype is a Volvo truck-trailer. The trailer is mounted by three flaps at the rear sides and top end. The actuators consist of loudspeakers in sealed cavities, connected to amplifiers that are supplied with a frequency generator controlled by LabVIEW. The full-scale test includes passive and active flow control investigations by varying the flap angle, with and without AFC, investigating different frequency and slot angle configurations. The fuel flux was measured during the full-scale test. The test shows a fuel reduction of about \(4\,\%\) in a comparison of two flap angles. The test of active flow control shows a reduction of \(5.3\,\%\) compared to the corresponding unforced case. Compared with the baseline case, the passive flow control fails to reduce the total fuel consumption.

Comparison studies have been conducted on a 1:16th scale model and a full scale tractor trailer of a variety of sealed aft cavity devices as a means to develop or enhance commercial drag reduction technology for class 8 vehicles. Eight base cavity geometries with pressure taps were created for the scale model. Drag data were acquired on the models using a 6-axis internal force balance for a range of yaw sweeps and at three Reynolds numbers for each base cavity. Pressure surveys for selected base cavities were also completed for the same yaw angles and Reynolds numbers to quantify the change in base pressure. The scale model force data indicated a marked decrease in drag at up to 12 % for two base cavity shapes, however most base cavities reduced drag by 3–10 % and a few did not decrease drag any significant amount. Pressure data indicated the base cavities increased the base pressure over baseline with a \(\Delta \mathrm{{C}}_\mathrm{{P}}\) of up to 0.3. Moreover, drag computed from pressure data implied that although the base cavities decreased the base drag due to a pressure increase, the drag may have increased elsewhere on the model. Full-scale tests were also completed using SAE Type II testing procedures. Full-scale tests on the same geometry indicated a fuel savings of over 6.5 %. Overall, the use of these devices shows to be a viable, effective and economical way to reduce fuel consumption on ground transport vehicles.

The trucking industry is moving into a new era of development brought on by governmental concerns over energy independence as well as the realities of increasing fuel costs. This has renewed interest in optimizing the aerodynamics of Class 8 tractor-trailer trucks. However, many of the large aerodynamic gains have already been developed, for example trailer skirts and boat tails that give fuel economy improvements of approximately 5 %. Research continues in order to better understand the aerodynamics of these vehicles and further improve their efficiency. Scale model rolling road testing has been around for several decades. In fact, the earliest rolling road wind tunnel test of a Class-8 truck that the authors are aware of occurred in the late 1980s [1]. In order to define the performance of a heavy duty truck, it has been well established that the use of wind averaged drag coefficients are required. To achieve wind averaged drag coefficients, it is necessary to measure data with a model in yaw for either a static floor or rolling road tunnel. The authors previously published results comparing a generic truck model tested using both a moving ground plane and a static ground plane. This paper builds on the work using a more detailed and modern truck model. The improvements in aerodynamic drag by fitting trailer skirts are discussed. These drag reductions are converted into fuel efficiency improvements and are compared to SAE type II testing. The reader will be able to appreciate the difficulty associated with attempting to correlate wind tunnel results to SAE Type II results. Some of the issues related to scale model rolling road testing such as Reynolds number dependency and yaw over a rolling road will be explored. Due to the size and nature of heavy duty trucks, cross winds must be taken into account. In addition to track or on-road testing, static tunnels have been the primary experimental tool for developing heavy duty trucks. Using the static floor tunnel method, heavy duty truck models have fixed (non-rotating tires) and are yawed via a turn table mounted in the floor of a tunnel. Multiple studies have been published which illustrate the necessity for rotating the tires in order to achieve improved correlation to real-world results, for examples see [1, 3‐6].

In ongoing studies on drag reducing devices for heavy vehicles wind tunnel experiments have been carried out at the Hermann-Föttinger Institute of the TU-Berlin. However, these wind tunnel experiments lack a moving belt or a suction system to remove the boundary layer of the wind tunnel floor. Therefore, the use of a towing tank which is available at the TU-Berlin was considered and realized. In order to gain experience with the towing tank as a tool for vehicle aerodynamic studies, preliminary experiments with a bluff body with out any ground effect were carried out. The box-shaped body corresponds to a simplified European trailer at a scale of 1:10. Towing speeds of up to 4 m/s leading to a Reynolds number of Re \(=\) 5.2 \(\times \) 10\(^6\) were used. Comparative measurements in the wind tunnel and the towing tank were carried out with the box. They showed good agreement, however maximum deviations of up to 2.5 % for the axial drag coeefficient were observed. The effect of passive drag reducing devices, so called base flaps, were measured and also their positive effect was well reproduced in the towing tank. The towing tank has thus been established as an aerodynamic test facility.

The paper discusses an appropriate usage of large eddy simulation (LES) in external vehicle aerodynamics. Three different applications including wheelhouse flow, gusty flow and active flow control, are used to demonstrate how LES can be used to obtain new knowledge about vehicle flows. The three examples illustrate the information that can be extracted using LES in vehicle aerodynamics.

Large-eddy simulation (LES) was used to study the flowaround a simplified tractor-trailer model. The model consists of two boxes placed in tandem. The front box represents the cab of a tractor-trailer road vehicle and the rear box represents the trailer. The LES was made at the Reynolds number of \(0.51 \times 10^6\) based on the height of the rear box and the inlet air velocity. Two variants of the model were studied, one where the leading edges on the front box are sharp and one where the edges are rounded. One small and one large gap width between the two boxes were studied for both variants. Two computational grids were used in the LES simulations and a comparison was made with available experimental force measurements. The results of the LES simulations were used to analyze the flow field around the cab and in the gap between the two boxes of the tractor-trailer model. Large vortical structures around the front box and in the gap were identified. The flow field analysis showed how these large vortical structures are responsible for the difference in the drag force for the model that arises when the leading edges on the front box are rounded and the gap width is varied.

Aerodynamic development of a full-scale truck presents a challenge for experimental testing due to the scale of the vehicle relative to most wind-tunnel test facilities. Numerical simulation is becoming more prevalent for assessing design changes and improving vehicle aerodynamic drag. In this process, the cumulative effects of small design changes are needed. Furthermore, the drag must be considered both at zero crosswind and with five degrees crosswind yaw angle in order to properly represent typical driving conditions. It is well-known that the aerodynamics of heavy trucks are complicated by a very transient wake flow that causes large fluctuations in base pressure, and therefore in the drag coefficient. This effect is often even more prevalent at non-zero yaw angles. The transient wake flow presents a challenge for effectively using simulation tools to predict the drag effects of small design changes, which may have some influence on the wake flow and base pressure.

A square back Ahmed body is used to mimic a heavy vehicle, bus or truck, in order to derive control processes that yield a significant drag reduction. The first step is to analyse carefully the structures in the flow that have a strong impact on the drag forces. Then, active and passive controls using blowing jets or porous medium layers are presented and discussed. The results are analyzed showing the direct impact of the control on the flow behaviour.

This paper describes a development program taking small scale Aerodynamic laboratory experimental technology to full-scale road tests. The fuel saving concept is based on attaching a 135 mm radius, quarter circle cross-section device, to the rear-side of truck-trailers. A full-scale conceptual prototype was designed and characterized by TAU and adopted as a full-scale adjustable and cost-effective prototype by ATDynamics. Bench-top tests at TAU validated the performance of the prototype as sufficient to warrant full-scale test success. Based on the bench-top tests it was decided that full scale inlet pressures of 3–6 psi at flow rates of 1–1.5 L/s per actuator are required. The full-scale prototype device comprised of some 100 suction and oscillatory blowing (SaOB) actuators’ array with a common compressed air supply. A positive displacement pump operated by a gasoline engine supplied the compressed air. As part of an ongoing ATD research project, a series of road tests were performed at the Goodyear Proving Ground, San Angelo, TX. Two identical trucks were tested. One truck-trailer was standard, while the other was equipped with the TAU-ATD device. Gauges located just downstream of the pump and at 5 locations along the supply ducts measured the supply pressures. Portable sensors measured the device suction pressure and pulsed blowing frequency. It was found that the pressure drop in the supply ducts was 10–15 %. However, additional 35 % pressure drop existed in the flexible tubes between the ducts and SaOB actuators. Out of the 81 possible configurations, determined by a 3 by 3 parameter space, 5 configurations were actually tested with valid results. One configuration, measured twice at a driving speed of 65 MPH, provided 5 % increase in fuel economy (not counting the input pump energy). This translates to a 1.75 L/100 km savings or 1 L/100 km taking into account the flow power invested. This improvement was obtained with inlet pressure lower than 4 psi, marginal according to all previous tunnel and bench-top tests. Furthermore, it is still open how close to optimal is this device configuration. With significantly reduced pressure losses, resulting in 5–6 psi inlet pressure at 15 % the current required input energy it is expected that 6–9 % net fuel saving would be obtainable in future road tests, potentially leading to the most compact commercial product to date.

The expected road transport demand in the next twenty years and the increasing environmental constraints together with the rising fuel prices has renewed the interest in truck design; any reduction in truck fuel consumption can be associated with large annual fuel cost reduction and considerable emission savings. Within the development of aerodynamic solutions numerical analysis tools, based on RANS equations, are often used to indicate flow phenomena and characteristics to design low drag bluff bodies. The presented work will discuss the similarities, but mainly the differences between wind tunnel experiments and the time-averaged numerical analysis. Rear pressure distributions are completely different when the numerical outcome is compared with the wind tunnel experiments. The CFD analysis of the boundary layer thickness is within acceptable resemblance with the wind tunnel measurements and the analytical power law model results. Stereoscopic PIV results show different wake structures.

The results of different approaches to quantitative flow visualization with large-scale capability are presented. The techniques were applied on the occasion of a measurement campaign in a medium-sized subsonic wind tunnel that addressed a passive wake control problem on an excursion boat. The obtained data was compared qualitatively with numerical results. Fluorescent tufts attached to the surface in the area of interest were filmed by a digital camera. Subsequent post-processing retrieved the local intensity variance and thus the tuft’s movement. This allowed for both, the identification of local flow direction and regions of detached flow on the surface of the model. Helium-filled soap bubbles were tracked using an asynchronous temporal contrast sensor or Dynamic Vision Sensor (DVS). The sensor is recording temporal changes in intensity only and has a high dynamic range which made it possible to track the bubbles in ambient light conditions. The recordings yielded local flow velocity and the streamlines around the model. The pressure field or local flow direction were recorded by tracking hand-held probes in 3D space with a stereo vision system. The system allowed free placement and fast measurements close to the model’s complex surface or in its wake. By moving the probe in the volume of interest and with suitable post-processing applied, a quick quantitative assessment of the pressure field and flow topology was possible. The application of the different techniques confirmed the potential of quantitative flow visualization in large-scale testing. The methods complemented each other in the sense that they served to extract surface flow, streamlines and pressure fields.