Parasite Drag Research Articles

Review on Vortex Generators Mounted on Airfoil to Improve the Aerodynamic Performance

In aircrafts lift is the most important factor which depends on wing performance. But during the cruising flight when the angle of attack increases there is change in the aerodynamic factors such as lift and drag forces due to the boundary layer (BL) separation. To delay or avoid this boundary layer separation and improve the aerodynamic performance of the wing vortex generators were introduced. Vortex generators helps to keep the boundary layer attached to the wings upper surface. In previous decades much study is done to control this BL on the different types of airfoils i.e. symmetrical or unsymmetrical. This review is based on study related to improve these parameters so that there will be increment in lift coefficient and reduction in drag coefficient. To overcome these parameters appropriate size, shape, length, position and incidence angle, etc should be investigated to find out the suitable one. These investigations can be performed as numerical based using software simulation and also by experimental approach in a wind tunnel. The main practical advantage of these vortex generators is to reduce parasite drag on airfoil and increase the lift force, they are also demonstrated to be critically important in other applications also.

Explorative gradient method for active drag reduction of the fluidic pinball and slanted Ahmed body

We address a challenge of active flow control: the optimization of many actuation parameters guaranteeing fast convergence and avoiding suboptimal local minima. This challenge is addressed by a new optimizer, called the explorative gradient method (EGM). EGM alternatively performs one exploitive downhill simplex step and an explorative Latin hypercube sampling iteration. Thus, the convergence rate of a gradient based method is guaranteed while, at the same time, better minima are explored. For an analytical multi-modal test function, EGM is shown to significantly outperform the downhill simplex method, the random restart simplex, Latin hypercube sampling, Monte Carlo sampling and the genetic algorithm. EGM is applied to minimize the net drag power of the two-dimensional fluidic pinball benchmark with three cylinder rotations as actuation parameters. The net drag power is reduced by 29 % employing direct numerical simulations at a Reynolds number of $100$ based on the cylinder diameter. This optimal actuation leads to 52 % drag reduction employing Coanda forcing for boat tailing and partial stabilization of vortex shedding. The price is an actuation energy corresponding to 23 % of the unforced parasitic drag power. EGM is also used to minimize drag of the $35^\circ$ slanted Ahmed body employing distributed steady blowing with 10 inputs. 17 % drag reduction are achieved using Reynolds-averaged Navier–Stokes simulations at the Reynolds number $Re_H=1.9 \times 10^5$ based on the height of the Ahmed body. The wake is controlled with seven local jet-slot actuators at all trailing edges. Symmetric operation corresponds to five independent actuator groups at top, middle, bottom, top sides and bottom sides. Each slot actuator produces a uniform jet with the velocity and angle as free parameters, yielding 10 actuation parameters as free inputs. The optimal actuation emulates boat tailing by inward-directed blowing with velocities which are comparable to the oncoming velocity. We expect that EGM will be employed as efficient optimizer in many future active flow control plants as alternative or augmentation to pure gradient search or explorative methods.

Bayesian Optimization of a Low-Boom Supersonic Wing Planform

A surrogate-assisted methodology to accelerate the design space exploration process and multi-objective optimization of a notional low-drag, low-boom supersonic transport planform using Euler computational fluid dynamics with an empirical parasite drag addition and an augmented Burgers equation solver is demonstrated. The use of Kriging-based surrogate models, coupled with expected hypervolume improvement in a Kriging believer framework, allows efficient global optimization of the selected wing design parameters. The use of effective nondominated sampling is used to further improve the solutions found. The effects of parameterizing the planform of a baseline model (NASA’s 69 deg wing–body) with 6- and 11-variables are explored. Genetic and local optimizers are used to search the Kriging surrogates. The results show the tradeoff between planform shapes that efficiently use compression lift to increase the lift-to-drag ratio and a smooth undertrack pressure signature to reduce ground-level noise. Furthermore, correctly positioned wingtips may also be used to smooth the undertrack signature, reducing the sonic boom.

Theoretical model proposal on direct calculation of wetted area and maximum lift-to-drag ratio

PurposeAs measuring flight performance by experimental methods requires a lot of effort and cost, theoretical models can bring new perspectives to aircraft design. This paper aims to propose a model on the direct calculation of wetted area and L/Dmax.Design/methodology/approachModel is based on idea that the wetted area is proportional to aircraft gross weight to the power of 2/3 (Wg2/3). Aerodynamic underpinning of this method is based on the square–cube law and the claim that parasitic drag is related to the Swet/Swing. The equation proposed by Raymer was used to find the L/Dmax estimate based on the calculated wetted area. The accuracy of the theoretical approach was measured by comparing the L/Dmax values found in the reference literature and the L/Dmax values predicted by the theoretical approach.FindingsProposed theoretical L/Dmax estimate matches with the actual L/Dmax data in different types of aircraft. Among the conventional tube-wing design, only the sailplanes have a very low Swet/Swing. The Swet/Swing of flying wings, blended wing bodies (BWBs) and large delta wings are lower than conventional tube-wing design. Lower relative wetted area (Swet/Swing) is the key design criterion in high L/Dmax targeted designs.Originality/valueThe proposed model could be used in wing sizing according to the targeted L/Dmax value in aircraft design. The approach can be used to estimate the effect of varying gross weight on L/Dmax. In addition, the model contributes to the L/Dmax estimation of unusual designs, such as variable-sweep wing, large delta wings, flying wings and BWBs. This study is valuable in that it reveals that L/Dmax value can be predicted only with aspect ratio, gross weight (Wg) and wing area (Swing) data.

Numerical modelling of vertical axis turbines using the actuator surface model

This paper presents the development and validation of a lightweight fluid solver based on the Navier–Stokes equations coupled to a special blade element method (BEM) for vertical axis turbines. This method is called Actuator Surface Model (ASM) and leads to a medium fidelity tool designed to bridge the gap between expensive blade resolving computational fluid dynamics (CFD) calculations and simple, often inaccurate momentum models such as the double-multiple streamtube (DMST) model. Since the simulation runs on coarse meshes, it is possible to use an explicit solver with a reasonable time step to significantly reduce the computing time to almost real-time speed. The fluid model is validated for the classical lid-driven cavity flow problem, while the coupled ASM code is compared with three different experimental measurements from the literature. For a more accurate description of blade specific phenomena, several higher order corrections were implemented, such as dynamic stall, parasitic drag and finite aspect ratio. The model is able to calculate the performance of all tested turbines reasonably well and can predict the maximum efficiency up to a few percent. Therefore it is an excellent alternative for a fast and precise initial design of vertical axis turbines compared to traditional BEM methods.

Full configuration drag estimation of short-to-medium range fixed-wing UAVs and its impact on initial sizing optimization

The paper presents the derivation of a new equivalent skin friction coefficient for estimating the parasitic drag of short-to-medium range fixed-wing unmanned aircraft. The new coefficient is derived from an aerodynamic analysis of ten different unmanned aircraft used for surveillance, reconnaissance, and search and rescue missions. The aircraft is simulated using a validated unsteady Reynolds-averaged Navier Stokes approach. The UAV’s parasitic drag is significantly influenced by the presence of miscellaneous components like fixed landing gears or electro-optical sensor turrets. These components are responsible for almost half of an unmanned aircraft’s total parasitic drag. The new equivalent skin friction coefficient accounts for these effects and is significantly higher compared to other aircraft categories. It is used to initially size an unmanned aircraft for a typical reconnaissance mission. The improved parasitic drag estimation yields a much heavier unmanned aircraft when compared to the sizing results using available drag data of manned aircraft.

Large Eddy Simulation of Microvortex Generators in a Turbulent Boundary Layer

Abstract This study investigates the flow physics on microvortex generators (MVGs) in order to improve their performance in turbulent boundary layers (TBLs). TBLs can be a challenging environment for MVGs because of the streamwise length of the generated vortex and the increased parasitic drag of the MVGs. Large eddy simulation (LES) is used to properly resolve the turbulent boundary layer of a flat-plate with a zero-pressure gradient and MVG vane. Three different vane-types are investigated (e423-Mod, triangular, and rectangular vanes) and are studied in a single vane configuration. Important flow features such as a separation bubble on the leading edge of the rectangular vanes which introduced unsteadiness into the vortex formation and degraded the MVG's efficiency was observed. The e423-Mod and triangular vanes were observed to be more aerodynamically efficient. The triangular vane was found to be the most efficient when evaluated immediately downstream of the vane. However, the vortex from the triangular vane decayed very rapidly due to it being formed very close to the wall which degraded its efficiency further downstream. The e423-Mod vane avoided this problem but its drag was very high relative to the strength of the generated vortex and its vortex experienced a brief period of rapid decay immediately downstream decreasing its efficiency. Further downstream, the vortex of the rectangular vane at 16 deg became the most efficient through a combination of low vane drag and low vortex decay in the TBL, demonstrating the need to consider a range of issues when designing an MVG.

Flow separation control using a bio-inspired nose for NACA 4 and 6 series airfoils

PurposeThis paper aims to achieve an optimum flow separation control over the airfoil using a passive flow control method by introducing a bio-inspired nose near the leading edge of the National Advisory Committee for Aeronautics (NACA) 4 and 6 series airfoil. In addition, to find the optimised leading edge nose design for NACA 4 and 6 series airfoils for flow separation control.Design/methodology/approachDifferent bio-inspired noses that are inspired by the cetacean species have been analysed for different NACA 4 and 6 series airfoils. Bio-inspired nose with different nose length, nose depth and nose circle diameter have been analysed on airfoils with different thicknesses, camber and camber locations to understand the aerodynamic flow properties such as vortex formation, flow separation, aerodynamic efficiency and moment.FindingsThe porpoise nose design that has a leading edge with depth = 2.25% of chord, length = 0.75% of chord and nose diameter = 2% of chord, delays the flow separation and improves the aerodynamic efficiency. Average increments of 5.5% to 6° in the lift values and decrements in parasitic drag (without affecting the pitching moment) for all the NACA 4 and 6 series airfoils were observed irrespective of airfoil geometry such as different thicknesses, camber and camber location.Research limitations/implicationsThe two-dimensional computational analysis is done for different NACA 4 and 6 series airfoils at low subsonic speed.Practical implicationsThis design improves aerodynamic performance and increases the structural strength of the aircraft wing compared to other conventional high lift devices and flow control devices. This universal leading edge flow control device can be adapted to aircraft wings incorporated with any NACA 4 and 6 series airfoil.Social implicationsThe results would be of significant interest in the fields of aircraft design and wind turbine design, lowering the cost of energy and air travel for social benefits.Originality/valueDifferent bio-inspired nose designs that are inspired by the cetacean species have been analysed for NACA 4 and 6 series airfoils and universal optimum nose design (porpoise airfoil) is found for NACA 4 and 6 series airfoils.

Impact of lift propeller drag on the performance of eVTOL lift+cruise aircraft

Electric vertical takeoff and landing (eVTOL) aircraft of the lift+cruise configuration are significantly impacted by the drag of the lift propellers even though they are only briefly used for takeoff and landing. This work aims to quantify the drag penalty of these high lift propellers, its impact on the performance of a lift+cruise eVTOL aircraft, and potential benefits from retracting the propellers during cruise. An eVTOL model is tested in the wind tunnel with propellers extended and retracted. Results show that retracting the propellers reduces parasitic drag by 38%. This measured drag reduction is used to estimate the performance of a passenger eVTOL and a surveillance drone employing a propeller retraction system. A passenger carrying eVTOL lift+cruise aircraft with a propeller retraction system could cruise 21% faster, at the same mission range, or increase range by 13% at the same flight speed. When endurance is the main mission objective, the benefits are smaller, in the order of 7%, and the potential gains are more sensitive to the weight of the retraction system.

Near wall coherence in wall-bounded flows and implications for flow control

Opposition-control of the energetic cycle of near wall streaks in wall-bounded turbulence, using numerical approaches, has shown promise for drag reduction. For practical implementation, real-time opposition control is only realizable if there is a degree of coherence between the turbulent velocities passing a sensor and the target point within the flow; for practicality, a sensor (and actuator) should be wall-based to avoid parasitic drag. As such, we here inspect the feasibility of real-time control of the near wall cycle, by considering the coherence between a measurable wall-quantity, being the wall-shear stress fluctuations, and the streamwise and wall-normal velocity fluctuations in a turbulent boundary layer. Synchronized spatial and temporal velocity data from two direct numerical simulations and a fine large eddy simulation at Reτ≈590 and 2000 are employed. This study shows that the spectral energy of the streamwise velocity fluctuations that is stochastically incoherent with wall signals is independent of Reynolds number in the near wall region (up to the viscous-scaled wall-normal height z+≈20). Consequently, the streamwise energy-fraction that is stochastically wall-coherent grows with Reynolds number due to the increasing range of energetic large scales. This thus implies that a wall-based control system has the ability to manipulate a larger portion of the total turbulence energy at off-wall locations, at higher Reynolds numbers, while the efficacy of predicting/targeting the small scales of the near wall cycle remains indifferent with varying Reynolds number. Coherence values of 0.55 and 0.4 were found between the streamwise and wall-normal velocity fluctuations at the near wall peak in the energy spectrogram, respectively, and the streamwise fluctuating friction velocity. These coherence values, which are considerably lower than 1 (maximum possible coherence) suggest that a closed-loop drag reduction scheme targeting near wall cycle streaks alone (based on sensed friction velocity fluctuations) will be of limited success in practice.

Ship Hull Resistance Prediction from Model Tests with a Resistance Similitude Simulator

Depending on model sizes and test speeds, model Reynolds numbers are typically one to two orders of magnitude less than those occurring at full scale. The region of laminar flow is significantly larger on a model surface than at full scale. Turbulence stimulators (TSs) are extensively applied in model resistance tests to simulate ship boundary layer flow. Because of lack of theoretical guidance, the size, shape, and location of turbulent stimulators used in each test facility are typically selected based on experience gained in each laboratory, and parasitic drag induced by TSs is subtracted from measured model resistance in some test facilities and not subtracted in other facilities. If turbulence stimulation can be specified in such a way as to achieve momentum thickness similarity between the model and full scale, the form factor will be constant, so a simple scaling formula can be applied to predict ship resistance. Ship resistance can be predicted from measured model resistance with the application of this simple scaling formula. The article describes how for a given body geometry, ship Reynolds number and model Reynolds number, a unique TS (size, shape, and location) can be designed based on three equations derived in this article. This uniquely designed TS is termed the "resistance similitude simulator" in this article. The parasitic drag induced by the simulator is a part of the similarity solution and does not need to be subtracted from measured model resistance. 1. Introduction The ability to predict resistance plays an important role in the design of a ship or submarine. An accurate prediction of the drag of the vessel is required for the propulsor design and to determine the required power. The resistance of the vessel also strongly influences its lifetime operation costs. Although computational methods are now commonly used to estimate ship resistance, model tests are still heavily relied on, and scaling formulae are used to relate model data to full-scale performance.

Conceptual design analysis of a variable swept half-span wing of a supersonic business jet

Supersonic business jets have a huge market potential, but face strict economic and environmental requirements. To guarantee the viability of the project, it must balance aerodynamic efficiency and low sonic boom intensity when operating in supersonic cruise. This paper describes the concept of an aircraft with one fixed low-swept half-span wing and one variably-swept half-span wing. Its aerodynamics will be studied in subsonic and supersonic regimes by both analytical methods, and numerical methods developed by the authors. The volumetric wave drag is evaluated numerically, through a method based on the linearized supersonic area rule, properly implemented in a VBA routine, coupled with a cone-based area extraction routine, implemented in a three-dimensional CAD environment. The study is divided in three separate fronts: first, the behavior of the wave drag with respect to the angle of sweep of the variable half-span wing; second, the influence of the tail configuration in both subsonic and supersonic parasite drag; and third, a comparison between different wing configurations. Results show that the proposed half-span variably-swept wing configuration is a promising alternative to operations flown in low supersonic Mach numbers over land, presenting a good aerodynamic efficiency, simultaneously with low-boom intensity.

Early Design Stage Evaluation of Thermal Performance of Battery Heat Acquisition System of a Hybrid Electric Aircraft

Abstract The electric energy and power storage, conversion and distribution (ESC&D) system of a hybrid electric aircraft, even at high efficiency, will reject significant heat at relatively low temperature. Thermal management systems (TMSs) can add excessive weight (heat exchangers and pumps) and impose excessive parasitic power consumption (pumps and fans) and drag (engine fan stream air and ram air) on the aircraft. Thus, effective low-weight thermal management of the ESC&D system is critical to realizing the potential benefits of a hybrid electric aircraft. This paper carries out early design stage benchmarking and evaluation of various thermal management approaches for the battery heat acquisition system of a hybrid electric aircraft. It is shown that the battery heat acquisition system based on state-of-the-art automotive electric vehicle design may be a third of the weight of the battery itself. Alternative approaches discussed here have the promise of reducing this weight by more than 60%.

An immersed lifting and dragging line model for the vortex particle-mesh method

The numerical study of the wake of full-scale slender devices such as aircraft wings and wind turbine blades requires high-fidelity large eddy simulation tools. The broad spectrum of scales involved entails the use of coarse-grain models for the devices. Actuator disk or line methods have been developed for that purpose, and are to date the most employed in that context. These methods transfer the force from the device to the fluid using 3D mollification functions. A novel immersed lifting and dragging line method is here presented, together with its implementation in a hybrid vortex particle-mesh flow solver. The line models the effect of blades or wings on the flow through the generation of vorticity, in a Lagrangian manner. This has several advantages over the treatment inherent to actuator methods: The absence of mollification in the spanwise direction and the relaxation of the classical Courant–Friedrichs–Lewy condition contribute to keeping the accuracy and the efficiency at a high level. The method is thoroughly verified against theory using results on various airfoils and wings. Finally, the efficiency of the approach is illustrated with the simulation of the wake of an elliptical wing. The role of parasitic drag in the development of wake instabilities is pointed out, by comparing configurations with none, moderate and high profile drag. In the last case, the simulation captures the fine scales vortex dynamics and the establishment of a turbulent wake over a length of 30 wing spans.

The Aerodynamics and Power Requirements of Forward Flapping Flight in the Mango Stem Borer Beetle (Batocera rufomaculata).

The need for long dispersal flights can drive selection for behavioral, physiological, and biomechanical mechanisms to reduce the energy spent flying. However, some energy loss during the transfer of momentum from the wing to the fluid is inevitable, and inherent to the fluid-wing interaction. Here, we analyzed these losses during the forward flight of the mango stem borer (Batocera rufomaculata). This relatively large beetle can disperse substantial distances in search of new host trees, and laboratory experiments have demonstrated continuous tethered flights that can last for up to an hour. We flew the beetles tethered in a wind tunnel and used high-speed videography to estimate the aerodynamic power from their flapping kinematics and particle image velocimetry (PIV) to evaluate drag and kinetic energy from their unsteady wakes. To account for tethering effects, we measured the forces applied by the beetles on the tether arm holding them in place. The drag of the flying beetle over the flapping cycle, estimated from the flow fields in the unsteady wake, showed good agreement with direct measurement of mean horizontal force. Both measurements showed that total drag during flight is ∼5-fold higher than the parasite drag on the body. The aerodynamic power estimated from both the motion of the wings, using a quasi-steady blade-element model, and the kinetic energy in the wake, gave mean values of flight-muscle mass-specific power of 87 and 65 W kg muscle-1, respectively. A comparison of the two values suggests that ∼25% of the energy is lost within the fluid due to turbulence and heat. The muscle mass-specific power found here is low relative to the maximal power output reported for insect flight muscles. This can be attributed to reduce weight support during tethered flight or to operation at submaximal output that may ensure a supply of metabolic substrates to the flight muscles, thus delaying their fatigue during long-distance flights.

EXPERIMENTAL ANALYSIS OF BLENDED WING BODY MODEL MICRO AIR VEHICLE USING WIND TUNNEL

An experimental aerodynamic analysis is performed to obtain aerodynamic characteristics and performance of a blended wing-body aircraft (BWB) using Low Speed Wind Tunnel. The BWB design concept is a revolutionary way of understanding the hike of fuel cost, increase in air travelers and environmental concern. Recognizing the potential of the aircraft an experimental analysis is conducted on BWB to understand aerodynamic performance parameters like lift coefficient (CL), drag coefficient (CD) and the Lift-to-Drag (L/D) ratio .The aluminium BWB model is manufactured using CNC machine and is tested in Wind tunnel at different angle of attack varying from 0° to 16° at speed of 12 m/s ,25 m/s and 35 m/s velocity. The present BWB UAV design has achieved an unprecedented capability in terms of sustainability of flight at high angle of attack, low parasite drag coefficient and decent maximum lift coefficient. This study indicates some significant benefits for the BWB relative to the conventional aircraft configuration. KEYWORDS: Blended Wing Body (BWB), Aerodynamics, Unmanned Aerial Vehicle (UAV), Wind Tunnel

Hydrodynamic Lubricant Film Separation During Codirectional and Counter-Directional Rotations of Disengaged Wet Clutch Packs

Abstract The parasitic drag losses incurred by wet clutches, used in transmission systems, can significantly affect vehicular powertrain efficiency. This paper presents a novel implicit solution for hydrodynamic parasitic drag losses of disengaged clutches. These are generated by conjunctional friction, taking into account lubricant film separation during codirectional and counter-directional disk pair rotations. Lubricant film rupture is considered through application of incipient reverse flow boundary condition, which is representative of lubricant film separation. The results point to the operating conditions at which significant power losses occur. In particular, the time efficient model is able to represent the small losses incurred during codirectional rotation of disk pairs.

Characterizing Influence of Transition to Turbulence on the Propulsive Performance of Underwater Gliders

Two models of underwater gliders were tested in a wind tunnel: one corresponding to a legacy shape commonly used in contemporary vehicles and the other a scaled down version of a new design. Performance of the two vehicles was characterized over a range of speeds and angles of attack. Particular attention was paid to the effect of sharp features along the hulls of the two vehicles and how they affect the observed flow regime. It has been shown that the new design, which uses a bow shape designed to encourage natural laminar flow, benefits from a 10% reduction of parasitic drag and 13% increase in lift-to-drag when the hull surface is smooth. The legacy glider, made up of a faired bow and a cylindrical hull, suffers from laminar separation and up to 100% increase in induced drag if the flow over its bow is prevented from transitioning to a turbulent state before encountering adverse pressure gradient at lower Reynolds numbers. This results in lowering of attainable speed at shallow glide path angles, whereas the associated parasitic drag reduction is demonstrated to increase the maximum velocity of the glider when moving at glide slopes greater than approximately 30°. 1. Introduction Underwater gliders are autonomous underwater vehicles (AUVs) that rely on using a buoyancy engine to ascend or descend through the water column, and by adjusting their pitch, they can use this vertical motion to develop forward thrust from their hydrofoils. This propulsion method allows them to undertake long-endurance missions, often several months long (Eriksen 2003; Rudnick et al. 2004; Graver 2005). Hydrodynamic performance of an underwater glider is primarily governed by its lift-to-drag (L/D) ratio, which dictates the minimum glide path angle the vehicle may adopt, and drag coefficient, which affects the maximum forward speed the glider may achieve for a fixed amount of vertical force developed (Graver 2005). It is thus important to minimize the drag of the AUV to allow it to perform longer deployments and gather more science data without increasing the size of the engine. Because of the typical Reynolds numbers on the vehicle hulls being less than 106 and of the order of 104–5 on the appendages, laminar and transitional flow regions may occur. Correctly identifying these is critical to achieve a robust performance prediction.

Flow separation control of NACA-2412 airfoil with bio-inspired nose

PurposeThe purpose of this paper is to achieve an optimum flow separation control over the airfoil using passive flow control method by introducing bio-inspired nose near the leading edge of the NACA 2412 airfoil.Design/methodology/approachTwo distinguished methods have been implemented on the leading edge of the airfoil: forward facing step, which induces multiple accelerations at low angle of attack, and cavity/backward facing step, which creates recirculating region (axial vortices) at high angle of attack.FindingsThe porpoise airfoil (optimum bio-inspired nose airfoil) delays the flow separation and improves the aerodynamic efficiency by increasing the lift and decreasing the parasitic drag. The maximum increase in aerodynamic efficiency is 22.4 per cent, with an average increase of 8.6 per cent at all angles of attack.Research limitations/implicationsThe computational analysis has been done for NACA 2412 airfoil at low subsonic speed.Practical implicationsThis design improves the aerodynamic performance and increases structural strength of the aircraft wing compared to other conventional high-lift devices and flow-control devices.Originality/valueDifferent bio-inspired nose designs which are inspired by the cetacean species have been analysed for NACA 2412 airfoil, and optimum nose design (porpoise airfoil) has been found.

Study of Brake Wear Particle Emissions: Impact of Braking and Cruising Conditions.

A novel measurement setup is designed, constructed, and validated by theoretical simulations and by experiments enabling sensitive and loss-free brake particle emission investigations. With the goal to simulate realistic driving, a 3 h subsection of the Los Angeles City Traffic (LACT) cycle is selected as test cycle. The tests are performed with the front brake of a midsize passenger vehicle under both static laboratory and more dynamic realistic conditions that include parasitic drag and vehicle brake temperatures (advanced vehicle simulations). A PM10 emission factor of around 4.6 mg km-1 brake-1 is determined. During five cycle runs the emission factor in terms of particle number decreases by 1 order of magnitude. This decrease is accompanied by a shift of the critical brake temperature Tcrit, at which ultrafine particle emissions occur, from 140 to 170 °C. Investigations with advanced vehicle simulations generate brake temperatures below Tcrit and consequently do not show ultrafine particle emissions above background level. A particle number emission factor of approximately 4.9 × 1010 km-1 brake-1 is estimated for realistic vehicle brake temperatures. Particle formation during cruising is clearly identified. The brake drag is estimated to contribute about 34% to the total airborne particle mass emission.