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Today CFD is an important tool for engineers in the automotive industry who model and simulate fluid flow. For the complex field of Under hood Thermal Management, CFD has become a very important tool to engineer the cooling airflow... more
Today CFD is an important tool for engineers in the automotive industry who model and simulate fluid flow. For the complex field of Under hood Thermal Management, CFD has become a very important tool to engineer the cooling airflow process in the engine bay of vehicles. To model the cooling airflow process accurately in CFD, it is of utmost importance to model all components in the cooling airflow path accurately. These components are the heat exchangers, fan and engine bay blockage effect. This paper presents CFD simulations together with correlating measurements of a cooling airflow system placed in a test rig. The system contains a heavy duty truck louvered fin radiator core, fan shroud, fan ring and fan. Behind the cooling module and fan a 1D engine silhouette is placed to mimic the blockage done by a truck engine behind the fan. Furthermore a simple hood is mounted over the module to mimic the air guiding done by the hood in an engine bay. The measurements monitor pressure and flow over the system. Supporting this examination is a set of 48 velocity probes in the radiator that measures the local velocity. The simulations of this system are correlated to measurements. Furthermore to support these simulations, specific simulations and measurements are conducted using the radiator only and the fan only. This is done to see how well each separate component is predicted in CFD and correlated back to measurements. This work is the continuation of work presented in [5] and identified in this paper is that one can simulate the cooling airflow system rather well with steady state CFD. However, fan modeling is sensitive and specific care has to be taken in order for these simulations to be accurate.
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ABSTRACT To fine tune the aerodynamic properties of road going vehicles the flow along the underbody is of outmost importance. Hence moving ground facilities has been introduced. In full-width mono-belt facilities the test vehicle is most... more
ABSTRACT To fine tune the aerodynamic properties of road going vehicles the flow along the underbody is of outmost importance. Hence moving ground facilities has been introduced. In full-width mono-belt facilities the test vehicle is most often suspended over the ground plane by a sting system. To mount the wheels, two possibilities exist. The designer of the wind tunnel model is faced with the choice to have the wheels on or off the model. The first option gives the most satisfying boundary conditions from a fluid dynamics point of view, however, the designer will face the problem of creating a frictionless chassis suspension system for the model. The “wheels off” type does not require such complex system but unfortunately creates a non-realistic flow due to the presence of so called wheel struts that carries the wheels. In the present work a numerical study of the flow around a “wheels off” model has been conducted. The study was performed to quantify how the presence of the wheel struts would affect the flow field and hence how this influence flow related measurements made on the model. The work has been done using a commercial CFD-code, running a standard k-epsilon model on a let-dominated mesh, counting roughly 6.5 million cells. As expected the flow field in the vicinity of the wheels is affected due to the extra vorticity introduced by the struts. The modified pressure field alters the drag and of further significance is the influence from the wheel struts on the underbody flow field. It is shown that care must be taken in studies of underbody and later underhood flows, using a “wheels-off” configuration.
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ABSTRACT Automotive aerodynamics measurements and simulations now routinely use a moving ground and rotating wheels (MVG&RW), which is more representative of on-road conditions than the fixed ground-fixed wheel (FG&FW)... more
ABSTRACT Automotive aerodynamics measurements and simulations now routinely use a moving ground and rotating wheels (MVG&RW), which is more representative of on-road conditions than the fixed ground-fixed wheel (FG&FW) alternative. This can be understood as a combination of three elements: (a) moving ground (MVG), (b) rotating front wheels (RWF) and (c) rotating rear wheels (RWR). The interaction of these elements with the flow field has been explored to date by mainly experimental means.This paper presents a mainly computational (CFD) investigation of the effect of RWF and RWR, in combination with MVG, on the flow field around a saloon vehicle. The influence of MVG&RW is presented both in terms of a combined change from a FG&FW baseline and the incremental effects seen by the addition of each element separately.For this vehicle, noticeable decrease in both drag and rear lift is shown when adding MVG&RW, whereas front lift shows little change. The same trends are seen in both CFD and experimental data.The addition of MVG alone increases both drag and front lift, whereas rear lift decreases significantly. The addition of RWF alone has little effect on the global results (aside from lift), whereas the addition of RWR alone decreases both drag and rear lift significantly. Combining the incremental changes produces values that align well to the MVG&RW case, with the exception of front lift.This shows similar trends to previously published work, both the noticeable drag decrease due to the addition of MVG&RW, and the contributions of the individual components.
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Abstract A small and highly sensitive flow velocity sensor was designed and fabricated using silicon microelectronic technology. To determine the performance of this silicon sensor, comparisons with a conventional hot-wire sensor were... more
Abstract A small and highly sensitive flow velocity sensor was designed and fabricated using silicon microelectronic technology. To determine the performance of this silicon sensor, comparisons with a conventional hot-wire sensor were made in a well-defined two-...
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Amongst the aerodynamic devices often found on race cars, the diffuser is one of the most important items. The diffuser can work both to reduce drag and also to increase downforce. It has been shown in previously published studies, that... more
Amongst the aerodynamic devices often found on race cars, the diffuser is one of the most important items. The diffuser can work both to reduce drag and also to increase downforce. It has been shown in previously published studies, that the efficiency of the diffuser is a function of the diffuser angle, ground clearance and most importantly, the base pressure. The base pressure of a car is defined by the shape of the car and in particular the shape at the rear end, including the rear wheels. Furthermore, on most race cars, a wing is mounted at the rear end. Since the rear wheels and wing will influence the base pressure it is believed that, for a modern race car, there could be a strong interaction between these items and the diffuser.
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A small direction-sensitive double-chip silicon-based sensor has been designed and fabricated using microelectronic technology. To determine the performance of this sensor the Reynolds stresses in a two-dimensional flat plate boundary... more
A small direction-sensitive double-chip silicon-based sensor has been designed and fabricated using microelectronic technology. To determine the performance of this sensor the Reynolds stresses in a two-dimensional flat plate boundary layer were determined at a ...
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Reducing resistance forces all over the vehicle is the most sustainable way to reduce fuel consumption. Aerodynamic drag is the dominating resistance force at highway speeds, and the power required to overcome this force increases by the... more
Reducing resistance forces all over the vehicle is the most sustainable way to reduce fuel consumption. Aerodynamic drag is the dominating resistance force at highway speeds, and the power required to overcome this force increases by the power three of speed. The exterior body and especially the under-body and rear-end geometry of a passenger car are significant contributors to the overall aerodynamic drag. To reduce the aerodynamic drag it is of great importance to have a good pressure recovery at the rear. Since pressure drag is the dominating aerodynamic drag force for a passenger vehicle, the drag force will be a measure of the difference between the pressure in front and at the rear. There is high stagnation pressure at the front which requires a base pressure as high as possible. The pressure will recover from the sides by a taper angle, from the top by the rear wind screen, and from the bottom, by a diffuser. It is not necessarily the case that an optimized lower part of the rear end for a wagon-type car has the same performance as for a sedan or hatch-back car. This study focused on the function of an under-body diffuser applied to a sedan and wagon car. The diffuser geometry was chosen from a feasibility stand-point of a production vehicle such as a passenger car. The fluid dynamic function and theory of the automotive under-body diffuser working as a drag reduction device is discussed. The flow physics of the under-body and the wake was analyzed to understand the diffuser behaviour in its application to lift and drag forces on a vehicle in ground proximity. This work is mainly a numerical analysis that uses the traditional CFD approach from the automotive industry. Results from this study show a potential to reduce aerodynamic drag of the sedan car approximately 10%, and the wagon car by 2-3 %. The possible gain was much bigger for the sedan vehicle and the optimum occurs at a higher diffuser angle. This was most likely due to the fact that the sedan car in its original shape produced more lift force than the wagon, a wagon usually produces very little lift or even down-force. Lift forces were also reduced with the use of under-body covers with diffuser. The down-force increased, or lift force decreased, linearly with increased diffuser angle, and the trend was the same for both sedan and wagon rear ends. Flow analysis of the wake showed the importance of how the wake is balanced.
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A very small and highly sensitive flow velocity sensor has been designed and fabricated using silicon microelectronic technology. To determine the performance of this silicon sensor, comparisons with a conventional hot-wire sensor were... more
A very small and highly sensitive flow velocity sensor has been designed and fabricated using silicon microelectronic technology. To determine the performance of this silicon sensor, comparisons with a conventional hot-wire sensor were made in a well defined two ...
... 52 (1996) 51-58 An integrated pressure-flow sensor for correlation measurements in turbulent gas flows Edvard K~ilvesten a, Christian Vieider b ... of the flow sensor, the 300 /zm0 /zm 30/zm heated chip, is defined and thermally... more
... 52 (1996) 51-58 An integrated pressure-flow sensor for correlation measurements in turbulent gas flows Edvard K~ilvesten a, Christian Vieider b ... of the flow sensor, the 300 /zm0 /zm 30/zm heated chip, is defined and thermally insulated by polyimide-filled KOH-etched trenches ...
Research Interests: Materials Engineering, Mechanical Engineering, Mechanics, Turbulent boundary layer, Flow measurement, and 11 moreTurbulent Flow, Steady state, Constant Time Delay, Pressure Sensor, Correlation coefficient, Boundary Layer, Wall Shear Stress, Gas Flow, Frequency Response, Electrical And Electronic Engineering, and Power Dissipation
Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 μm, that... more
Manufacturing processes that can create extremely small machines have been developed in recent years. Microelectromechanical systems (MEMS) refer to devices that have characteristic length of less than 1 mm but more than 1 μm, that combine electrical and mechanical ...
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In the current study the wall jet flow of high Reynolds number is investigated. As presented experimental and DNS results demonstrate, for such operating conditions a laminar flow similarity is not reached due to the happening flow... more
In the current study the wall jet flow of high Reynolds number is investigated. As presented experimental and DNS results demonstrate, for such operating conditions a laminar flow similarity is not reached due to the happening flow breakdown and the three-dimensional effects are important. For the purpose of linear stability investigation, the problem of the flow description is resolved and
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This paper presents a detailed experimental evaluation of the flow field in a state of the art linear cascade with boundary-layer suction. The linear cascade was designed using a new design-process as described by Hjarne et al. [1]. From... more
This paper presents a detailed experimental evaluation of the flow field in a state of the art linear cascade with boundary-layer suction. The linear cascade was designed using a new design-process as described by Hjarne et al. [1]. From the measurements presented in this paper it can be concluded that all of the features of the test-rig work as expected. Hence the measurements validate the design process presented by Hjarne et al. in [1].The intention with the test facility is to provide high quality benchmark cases for the flow field around aggressive designs of Low Pressure Turbine/Outlet Guide Vanes (LPT/OGV's) to be used for validation of numerical codes. The flow quality is assessed by measuring inlet uniformity, boundary-layer heights, periodicity of the static pressure distribution around the OGV's and uniformity of the outlet flow.
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In the current study the wall jet flow of high Reynolds number is investigated. As presented experimental and DNS results demonstrate, for such operating conditions a laminar flow similarity is not reached due to the happening flow... more
In the current study the wall jet flow of high Reynolds number is investigated. As presented experimental and DNS results demonstrate, for such operating conditions a laminar flow similarity is not reached due to the happening flow breakdown and the three-dimensional effects are important. For the purpose of linear stability investigation, the problem of the flow description is resolved and a boundary-layer solution developing from coupled Blasius boundary layer and Blasius shear layer is implemented, valid in the close downstream field of a slot. Performed linear stability investigations reveal the high instability of two-dimensional eigenmodes and non-modal streaks, and the calculations agree reasonably well with the provided experiments. Furthermore, the nonlinear stage of laminar flow breakdown is studied both with three-dimensional direct numerical simulation and experimentally. A modelling of the "natural" experimental case is achieved using random noise simulations ...
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A plane wall-jet flow is numerically investigated and compared to experiments. The measured base flow is matched to a boundary-layer solution developing from a coupled Blasius boundary layer and Blasius shear layer. Linear stability... more
A plane wall-jet flow is numerically investigated and compared to experiments. The measured base flow is matched to a boundary-layer solution developing from a coupled Blasius boundary layer and Blasius shear layer. Linear stability analysis is performed, revealing high instability of two-dimensional eigenmodes and non-modal streaks. The nonlinear stage of laminar-flow breakdown is studied with three-dimensional direct numerical simulations and experimentally visualized. In the direct numerical simulation, an investigation of the nonlinear interaction between two-dimensional waves and streaks is made. The role of subharmonic waves and pairing of vortex rollers is also investigated. It is demonstrated that the streaks play an important role in the breakdown process, where their growth is transformed from algebraic to exponential as they become part of the secondary instability of the two-dimensional waves. In the presence of streaks, pairing is suppressed and breakdown to turbulence ...
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Wind-tunnel data on velocity perturbations evolving in a laminar swept-wing flow under low subsonic conditions are reported. The focus of the present experiments are secondary disturbances of the boundary layer which is modulated by... more
Wind-tunnel data on velocity perturbations evolving in a laminar swept-wing flow under low subsonic conditions are reported. The focus of the present experiments are secondary disturbances of the boundary layer which is modulated by stationary streamwise vortices. Both the stationary vortices and the secondary oscillations of interest are generated in a controlled manner. The experimental data are obtained through hot-wire measurements. Thus, evolution of the vortices, either isolated or interacting with each other, is reconstructed in detail. As is found, the secondary disturbances, initiating the laminar-flow breakdown, are strongly affected by configuration of the stationary boundary-layer perturbation that may have an implication to laminar–turbulent transition control. Graphical abstract
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Nonlinear instabilities of boundary layer streaks are investigated experimentally. Extensive measurements visualizing the sinusoidal and varicose instabilities of streaky structures at nonlinear stage of the breakdown process in boundary... more
Nonlinear instabilities of boundary layer streaks are investigated experimentally. Extensive measurements visualizing the sinusoidal and varicose instabilities of streaky structures at nonlinear stage of the breakdown process in boundary layer are presented. The flow behaviour in the course of spatial evolution of the streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaks are demonstrated, such as transverse and streamwise modulations of the streak by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady Λ-shaped structures localized in space in both cases.
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Page 1. An analytical asym ptotic solution to a conjugate heat transfer problem Carl Fredrik Stein Department of Mathematics, Chalmers University of Technology S-412 96 G{oteborg, Sweden e-mail: stein@math.chalmers.se tel. +46 31 772 53... more
Page 1. An analytical asym ptotic solution to a conjugate heat transfer problem Carl Fredrik Stein Department of Mathematics, Chalmers University of Technology S-412 96 G{oteborg, Sweden e-mail: stein@math.chalmers.se tel. +46 31 772 53 44, fax. +46 31 16 19 73 ...
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An experimental investigation was carried out to assess the drag reducing potential of active flow control in conjunction with flat panel flaps attached to the trailer of a generic tractor–trailer model. The experiments were carried out... more
An experimental investigation was carried out to assess the drag reducing potential of active flow control in conjunction with flat panel flaps attached to the trailer of a generic tractor–trailer model. The experiments were carried out in a wind tunnel with a 1/10th scale generic tractor-trailer model at Reynolds numbers up to 640,000 based on the model width. Active flow control was achieved by means of constant blowing, constant suction and oscillatory blowing and suction. A secondary objective was to make short base flaps with active flow control as effective as long flaps with no active flow control. Measurement techniques such as flow visualizations, loads by means of a 6-component balance, LDA and PIV were employed. The results show that constant blowing at a momentum coefficient of 11.13% is able to achieve higher drag reduction than long flaps with no active flow control. The analysis of the flow field in the wake showed that constant blowing deflects the shear layer between the free stream and the wake region downward and hence reduces the size of the wake. The flaps at the side of the truck did not appear to have any substantial drag reducing effect.