Dr Tariq Saeed: Swept-Wing Transition Experiment

imageTariq’s study focusses on the experimental investigation of the interaction of a 2D roughness strip and crossflow instabilities. The phases of the experimental programme are to: 1) measure the freestream disturbance environment of the wind tunnel; 2) quantify the base flow, which is forced using discrete roughness elements; and 3) study how boundary-layer instabilities are affected by the introduction of a 2D roughness strip.


The “AERAST” swept wing model used for investigations is provided by Airbus. It has been designed to enhance the growth of the crossflow instability, and has a sweep-back angle of 40 degrees. The experiment is performed in the Automotive Wind Tunnel at BMT Fluid Mechanics Ltd. The tunnel is a closed-loop facility with a working test-section of 2.3 m x 1.8 m x 6.0 m. The tunnel can reach speeds of up to 48 m/s (a unit Reynolds number 3.3 x 106 /m). The measured freestream turbulence intensity level is 0.10%.

Naphthalene surface flow visualisation is used to assess transition location and qualitatively examine the crossflow vortex wavelength. (See figure below) image



Detailed boundary-layer hotwire scans are performed along the span of the swept-wing model at various chordwise positions. Stationary crossflow information is extracted through examination of the mean flow statistics, whilst temporal r.m.s information is used to assess the travelling-wave crossflow mode. (See figure to the right for mean-flow velocity contour plot.)






Research outputs
Saeed, T. I., Morrison, J. F., and Mughal, M. S.,  “Roughness effects on swept-wing crossflow transition in moderate free-stream turbulence”, in 29th International Congress of Aeronautical Science, St. Petersburg, Russia , 2014, ICAS-2014-0542.

Swept Wing Experiment Industry Application

Richard Bosworth: Boundary Layer Receptivity to Freestream Disturbances

bosworth Richard’s research focuses on the experimental receptivity of a Blasius boundary layer to freestream disturbances. The study’s first aim is to investigate the excitation of Tollmien-Schlicting waves by the interaction between freestream convected gusts and roughness strips. The second is to investigate the change in receptivity as the forcing amplitude increases. Disturbance evolution is measured in the downstream direction on an aluminium flat plate using Hot-Wire Anemometry.


Transition from laminar to turbulent flow has a wide-ranging impact on drag and wear for many industrial processes and aviation. The aim of many transition studies is thus to find a method to predict, and/or control, the location of transition given a specific geometry. Receptivity is concerned with how small disturbances enter the boundary layer and provide the initial conditions for instabilities to grow. Gaining an understanding of these processes will help improve the methods of prediction and control currently in place. Richard's research will consist of introducing varied types of disturbance into the free stream and observing the response of the boundary layer.

The main method to explore this field will be experiments within the 3’ x 3’ wind tunnel in the aeronautics department. Hot-wire anemometry will be the main type of measurement technique and different disturbances will be introduced with either added turbulence screens or other localized sources.

R. Bosworth Project: Industry Application

Hari Vemuri - Tollmien-Schlichting wave cancellation by Feedback Control

vemuriHari's research focuses on active control of growing Tollmien-Schlichting waves in a Blasius boundary layer by making use of sensors and actuators connected in feedback on a flat plate model. The aims of this research are to: 1. achieve excitation of clean TS waves via a point source excited by a mini-speaker; 2. obtain the necessary transfer function models between the source and sensor and the actuator and sensor in order to design a controller; and 3. design and implement a controller to effect real-time attenuation of TS waves. A wall hot-wire sensor manufactured in-house is used for control and a second traversing hot-wire is used to record the performance of the control system downstream.


The active control approach in this work uses downstream sensor feedback to upstream actuators to control growing TS waves excited by a speaker on a flat-plate model. The key element of active control is the determination of the transfer functions of the control system connecting the sensors to the source (speaker) and the actuators. The numerical two- and three-dimensional transfer functions are obtained by solving the Orr-Sommerfeld equations These transfer functions are used to obtain the optimal sensor-actuator configurations by calculating the overall degree of control that can be achieved. These configurations are then tested in a wind-tunnel for real-time cancellation. image

H. Vemuri Project: Industry Application