Gallery

Below are some of our present projects. Click on the image to see the poster.

Controlling Wave Packets on Swept Wings On the problem of controlling travelling wave packets on an innite swept wing using linear control theory. Based on wall measurements , an extended Kalman lter is used to estimate the 3D wave packet. The estimated eld is in turn used to calculate a feedback control which changes the growth of the disturbance into decay.

Investigation of the Near-field of a Swirling Turbulent Jet Swirling jets are used in many engineering applications, because among other things it is known that rotating jets spread and mix with the ambient fluid faster than their non-swirling counterparts. Several advanced measurement techniques (HWA, LDV and stereoscopic- PIV) were used to investigate the turbulent velocity and temperature field in the near-field of a non-swirling and swirling free jet emanating from a 6m long axially rotating pipe flow.

Phase-Field Simulations of Free Boundary Free boundary flows are widespread in nature and in many areas of physical and biological sciences. The models that have been developed for free boundary problems can be classified into two types, sharp-interface models and diffuse-interface models. One type of diffuse-interface models of particular interest are phase-field based models.

Muscle Mechanics and Modelling As commonly used Hill-type muscular models are known to have their main shortcomings, we are particularly interested in the response from the muscles when activated in eccentric situations, i.e., situations of externally induced lengthening of the muscles during activation.The muscle is then forced to stretch, with a constant stretch velocity, and is then held isometrically again. of parameters, different model con gurations could be achieved.

Turbulent Flows Simulation and Modelling For Newtonian fluids the flow motion is described by the Navier-Stokes equations. In a Direct Numerical Simulation, DNS, the Navier-Stokes equations are solved numerically by discretization in both time and space. DNS of turbulent flows requires very high resolution. LES of homogeneous shear flow. LES, is an under-resolved numeric simulation of the Navier Stokes equation in which the influence of the non resolved, or subgrid, scales has to be modelled. Homogeneous shear flow is an excellent test case for developing and testing subgrid scale models. The simple geometry of the flow enables the use of the accurate spectral methods which makes it easy to separate model features from the numerical errors.

Simulation of Dielectrophoresis The subject of separating microsize particles with different properties is always of great interest. Among those methods, dielectrophoretic separation devices are most commonly used as trap-and-release filters or particle sorters.We simulate particles movements under dielectrophoresis force in different situations in this project

Fluid Mechanics for Better Paper Paper is made from a suspension of about 0.5% cellulose fibres and 99.5% water. In the first stage of a paper machine, this suspension is sprayed as a wide (up to 10 m) thin (about 1 cm) fast (up to 1800 m/min) jet on to wires, on which the paper is formed after removal of the water. The fluid mechanics of the initial forming is one of the major factors in fluencing the properties of the final paper.

Analysis of Shell, Membrane and Cable Structures The use of thin shells (membranes) and cables is increasing in both civil engineering and aerospace applications. Such structures experience significant geometric and material non-linear behaviour, which require efficient and robust nite elements and solution routines. This project concerns the analysis of complex instability in shells. The objective is to develop and implement efficient finite elements and path following procedures.

Optimality in Human Movement Analysis of gait and motion strategies, in both able-bodied persons and those with a pathology affecting the musculoskeletal system, is used to understand the central nervous system s solution for producing movement in the over-constrained human body. The use of movement analysis in prescribing treatment or predicting outcome, however, is limited by the current assessment-based interpretation approach.Mathematical modelling methods can provide an opportune complement to the current movement analysis techniques by quantifying the causal relationship between muscle activation and joint movement, and the motion strategy adopted in this redundant force system.

Extending the Navier-Stokes Equations to Smaller Length Scales When smaller length scales are important, the Navier-Stokes are no longer sufficient. The second approximation in the mean free path, the Burnett equations, is however unsatisfactory. The reason is that for very short length scales it is unstable. Here we show a way to stabilize the Burnett equations as equations for the five fluid dynamic variables.

Laminar wings on future aircrafts SUPERTRAC stands for SUPERsonic TRAnsition Control. Flying at supersonic speeds involves problems like for example noise and high fuel consumption. A reduction of the skin friction coef cient to reduce drag would improve on these problems. The objective for the SUPERTRAC project is to investigate various methods to delay transition from laminar to turbulent ow over the wings at supersonic speeds. These methods have been tested at subsonic speeds but little is known of their ef ciency at supersonic speeds. Both Airbus and Dassault have an interest to apply the techniques to improve on future supersonic passenger aircraft.

On Focusing of Strong Shock Waves Focusing of shock waves has many applications, ranging from medical treatments to cutting and cleaning of hard surfaces with water jets. Also, the non-linear dynamics that occur during the focusing process are of great interest. Experiments on shock wave focusing have been performed since the beginning of the 1950 s. To be able to study the whole focusing and re ecting process, a new shock tube was built at KTH Mechanics. The test section of the shock tube has an exchangeable re ector boundary and hence it is possible to use different shapes of re ectors to shape the shock wave.

Numerical Simulations of Transition and Turbulence A large share of the research in FluidMechanics at the Department of Mechanics is performed by means of direct numerical simulations (DNS). That is, the temporal and spatial evolution of the flow is obtained by numerical solution of the governing Navier-Stokes equations without any simplifying assumptions. This requires larger computational efforts, both in term of memory and effective time of the calculations, since all the relevant scales characterising the flow configuration under examination must be solved

Active Control of Thermocapillary Convection The optimal conditions are obtained by playing on sensors/heaters relative positions as well as on weights of linear, non-linear and derivative terms in the feedback law. Besides fundamental interests of control achievement in a benchmark ow, the study is motivated by practical purposes of eliminating striations during crystal productions and on undesirable ows in welding pools.

Using Pressure Sensitive Paint (PSP) in transonic flow Pressure sensitive paint is an optical method to obtain the pressure on an object surface without instrumenting the object. The surface is coated with a paint containing luminophore molecules (florescent or phosphorescent) and illuminated with light source emitting light of of sufficient short wavelength to excite the luminophore.