Vehicle surface contamination, unsteady flow and aerodynamic drag

The rear surfaces of blunt-ended vehicles, such as SUVs, are vulnerable to the build-up of contaminants thrown up from wet road surfaces by their tyres. This can compromise drivers’ vision, vehicle visibility, sensor performance and aesthetics. Vision will be reduced if the rear screen and lenses of camera systems become obscured. Similarly, sensing methods such as Light Detection and Ranging [LIDAR], introduced to support higher-level Advanced Driver Assistance Systems [ADAS] and autonomous driving are also vulnerable to contaminant accumulation. In addition, vehicle users may find that dirt is transferred to their hands and clothes as they access the rear load space. Finally, rapid soiling of external surfaces can be perceived as degrading the aesthetics of premium vehicles. Such deposition is a manifestation of unsteady aerodynamics – particularly the interaction between tyre spray, wheel wakes and the vehicle rear wake. These wake structures also strongly influence aerodynamic drag which, in turn affects CO2 emissions for Internal Combustion Engine [ICE] powered cars and the range of Battery Electric Vehicles [BEV]. Hence, automotive manufacturers need a simulation approach that can be used to minimise these characteristics concurrently during vehicle development. This work met that need by developing and deploying an innovative simulation process which predicts both contaminant accumulation and drag at the same time, by numerically representing unsteady aerodynamics, tyre spray and surface water behaviour. It is now integrated into the vehicle development process at Jaguar Land Rover [J/LR] where it is being used to develop new cars. This has been achieved by using a series of novel simplified vehicle geometry and spray systems to incrementally develop and validate the simulation strategy. The work culminated with its application to a production vehicle and subsequent validation against full scale experiments, providing the first quantification of accuracy for simulations of rear surface contamination. This novel simulation approach is combined with original experiments to show that reduced vehicle ride heights can lead to increased rear surface contamination, by reducing underbody flow and moving the vehicle wake closer to the highly contaminated wheel wakes. This provides a challenge for vehicle developers as lower ride heights are used to reduce aerodynamic drag; an increasingly important objective for both ICE and BEV product development, to support lower CO2 emissions and enhanced range, respectively. Finally, the first evidence is presented to suggest that aerodynamically improved underfloors can increase rear surface contamination, or at least redistribute it towards the lower regions of the vehicle rear, such as the bumper. This raises a risk for future BEVs which combine aerodynamically advantageous smooth underfloors with vulnerable ADAS features, such as rear bumper mounted LIDAR

Surface contamination of cars : a review

This review surveys the problem of surface contamination for cars, which poses a growing engineering challenge to vehicle manufacturers, operators and users. Both drivers’ vision and vehicle visibility need to be maintained under a wide range of environmental conditions. This requires managing the flow of surface water on wind screens and side glazing. The rate of deposition of solid contaminants on glazing, lights, license plates and external mirrors also needs to be minimised. Maintaining vehicle aesthetics and limiting the transfer of contaminants to the hands and clothes of users from soiled surfaces are also significant issues. Recently, keeping camera lenses clean has emerged as a key concern, as these systems transition from occasional manoeuvring aids to sensors for safety systems. The deposition of water and solid contaminants onto car surfaces is strongly influenced by unsteady vehicle aerodynamic effects. Airborne water droplets falling as rain or lifted as spray by tyres interact with wakes, vortices and shear flows and accumulate on vehicle surfaces as a consequence. The same aerodynamic effects also control the movement of surface water droplets, rivulets and films; hence, particular attention is paid to surface water management over the front side-glass and the deposition of contaminants on the rear surfaces. The test methods used in the automotive industry are reviewed, as are numerical simulation techniques

Parametric study of asymmetric side tapering in constant cross wind conditions

Sports Utility Vehicles (SUVs) often have blunt rear end geometries for design and practicality, which is not typically aerodynamic. Drag can be reduced with a number of passive and active methods, which are generally prioritised at zero yaw, which is not entirely representative of the “on road” environment. As such, to combine a visually square geometry (at rest) with optimal drag reductions at non-zero yaw, an adaptive system that applies vertical side edge tapers independently is tested statically. A parametric study has been undertaken in Loughborough University’s Large Wind Tunnel with the ¼ scale Windsor Model. The aerodynamic effect of implementing asymmetric side tapering has been assessed for a range of yaw angles (0°, ±2.5°, ±5° and ±10°) on the force and moment coefficients. This adaptive system reduced drag at every non-zero yaw angle tested, from the simplest geometry (full body taper without wheels) to the most complex geometry (upper body taper with wheels) with varying levels of success; providing additional drag reductions from 3% to 125%. The system also shows potential to beneficially modify the cross wind stability of the geometry

Influence of short rear end tapers on the unsteady base pressure of a simplified ground vehicle

Short tapered sections on the trailing edge of the roof, underside and sides of a vehicle are a common feature of the aerodynamic optimization process and are known to have a significant effect on the base pressure and thereby the vehicle drag. In this paper the effects of such high aspect ratio chamfers on the time-dependent base pressure are investigated. Short tapered surfaces, with a chord approximately equal to 4% of the overall model length, were applied to the trailing edges of a simplified passenger car model (the Windsor Body) and base pressure studied via an array of surface pressure tappings. Two sets of configurations were tested. In the first case, a chamfer was applied only to the top or bottom trailing edge. A combination of taper angles was also considered. In the second case, the chamfer was applied to the side edges of the model base, leaving the horizontal trailing edges squared. In all configurations both the base and the slanted surfaces were covered with pressure taps for the entire width to ensure that any asymmetry was captured and two different sampling time were considered (respectively equal to 31.5 s and 630.0 s). The results show the effects produced on the base pressure by the presence of a long period bi-stable behavior, whose characteristics were further investigated by conditional averaging the recorded data and considering the distribution of the rms pressure values recorded over the entire model base

The effect of passive base ventilation on the aerodynamic drag of a generic SUV vehicle

Sports Utility Vehicles (SUVs) typically have a blunt rear end shape (for design and practicality), however this is not beneficial for aerodynamic drag. Drag can be reduced by a number of passive and active methods such as tapering and blowing into the base. In an effort to combine these effects and to reduce the drag of a visually square geometry slots have been introduced in the upper side and roof trailing edges of a squareback geometry, to take air from the freestream and passively injects it into the base of the vehicle to effectively create a tapered body. This investigation has been conducted in the Loughborough University’s Large Wind Tunnel with the ¼ scale generic SUV model. The basic aerodynamic effect of a range of body tapers and straight slots have been assessed for 0° yaw. This includes force and pressure measurements for most configurations. The slots generate useful, but small, drag reductions with the best configurations giving reductions in drag coefficient (Cd) of approximately 0.01, whereas the best taper configurations reduce Cd by close to 0.035. The slots also have a tendency to modify the lift

Parametric study of asymmetric side tapering in constant cross wind conditions

Copyright © 2018 SAE International. Sports Utility Vehicles (SUVs) often have blunt rear end geometries for design and practicality, which is not typically aerodynamic. Drag can be reduced with a number of passive and active methods, which are generally prioritised at zero yaw, which is not entirely representative of the “on road” environment. As such, to combine a visually square geometry (at rest) with optimal drag reductions at non-zero yaw, an adaptive system that applies vertical side edge tapers independently is tested statically. A parametric study has been undertaken in Loughborough University’s Large Wind Tunnel with the ¼ scale Windsor Model. The aerodynamic effect of implementing asymmetric side tapering has been assessed for a range of yaw angles (0°, ±2.5°, ±5° and ±10°) on the force and moment coefficients. This adaptive system reduced drag at every non-zero yaw angle tested, from the simplest geometry (full body taper without wheels) to the most complex geometry (upper body taper with wheels) with varying levels of success; providing additional drag reductions from 3% to 125%. The system also shows potential to beneficially modify the cross wind stability of the geometry

Simulation of rear surface contamination for a simple bluff body

Predicting the accumulation of material on the rear surfaces of square-backed cars is important to vehicle manufacturers, as this progressively compromises rear vision, vehicle visibility and aesthetics. It also reduces the effectiveness of rear mounted cameras. Here, this problem is represented by a simple bluff body with a single sprayer mounted centrally under its rear trailing edge. A Very Large Eddy Simulation (VLES) solver is used to simulate both the aerodynamics of the body and deposition of contaminant. Aerodynamic drag and lift coefficients were predicted to within +1.3% and −4.2% of their experimental values, respectively. Wake topology was also correctly captured, resulting in a credible prediction of the rear surface deposition pattern. Contaminant deposition is mainly driven by the lower part of the wake ring vortex, which advects material back onto the rear surface. This leads to a maximum below the rear stagnation point and an association with regions of higher base pressure. The accumulation of mass is linear with time; the relative distribution changing little as the simulation progresses, implying that shorter simulations can be compared to longer experiments. Further, the rate of accumulation quickly reaches a settled mean value, suggesting utility as a metric for assessing different vehicles

Colorectal cancer in South Africa: An assessment of disease presentation, treatment pathways and 5-year survival

Background. Colorectal cancer (CRC) is the fourth most common cancer in South Africa (SA), and the sixth most lethal. Approximately 25% of patients will have synchronous metastatic disease at the time of their primary CRC diagnosis. Although chemotherapy is used in most stages of the disease, surgical resection of the primary tumour and metastases remains the most successful treatment modality to achieve cure or prolong survival. To date, no data on CRC presentation and management have been published in SA.Objectives. To determine CRC presentation, general management patterns and overall survival in the SA private healthcare sector.Methods. A retrospective review of a private healthcare funder’s database from 1 January 2008 to 31 December 2015. International Statistical Classification of Diseases and Related Health Problems (10th revision) (ICD-10) diagnosis codes were used to identify colorectal cancer and liver and/or pulmonary metastatic disease. Procedure codes assigned to hospital admissions were used to identify type of surgical treatment. Chemotherapy was identified by the World Health Organization Anatomical Therapeutic Chemical Classification System of medicines. Treatment patterns were determined and 5-year survival rates for these were calculated. Survival was estimated using the Kaplan-Meier method, and Cox proportional hazards regression was used for between-group comparisons of survival. Data analysis was carried out using SAS version 9.4 for Windows.Results. A total of 3 412 patients were included in the study, 2 267 with CRC only and 1 145 with liver (LM) or pulmonary metastases (PM). The mean age was 64.1 years (range 21 - 97), and 54.6% were male; these did not differ statistically between the study groups. Twenty percent of patients with LM or PM underwent surgical resection of their metastases. Five-year survival rates following surgical resection of all disease for CRC only, CRCLM, CRCPM and CRCLMPM were 71.7%, 57.3%, 31.5% and 26.0%, respectively.Conclusions. SA CRC patients treated in the private healthcare sector have similar disease presentation to that in published international series, with similar outcomes following various treatment pathways; however, it seems that fewer resections of metastases are undertaken compared with international trends.