Shuhaimi Mansor

Estimation of bluff body transient aerodynamics using an oscillating model rig

A method for the estimation of transient aerodynamic derivatives from dynamic wind tunnel tests using time response data is presented in this paper. For the purposes of the study, the aerodynamic derivatives are considered to act as a stiffness and damping to the model motion. The experimental set-up consists of a simple bluff body (Davis model) constrained to oscillate with a single degree of freedom of pure yawing motion. A range of springs were used to control the oscillation frequency and hence the reduced frequency. The transient responses from dynamic wind tunnel tests are compared with quasi-steady analysis in order to investigate the effect of unsteady aerodynamics. The aerodynamic derivatives are initially estimated using the classical logarithmic decay method. The dynamic stiffness derivative exceeds that determined statically across the reduced frequency range. The damping derivative was found to be a function of free-stream speed; at low velocities it is negative but progressively increases to a positive value. With further increases in speed, a self-sustained oscillation is observed with almost constant frequency and amplitude. This result is attributed to coupling between the model wake and the model stability; however, the exact mechanism of the interaction is not fully understood. This phenomenon is under further investigation.

The Measurement of Transient Aerodynamics Using an Oscillating Model Facility

A method for the estimation of transient aerodynamic data from dynamic wind tunnel tests has been developed and employed in the study of the unsteady response of simple automotive type bodies. The paper describes the facility and analysis techniques employed and reports the results of a parametric study of model rear slant angle and of the influence of C-pillar strakes. The model is shown to exhibit damped, self-sustained and self-excited behaviour. The transient results are compared with quasi-steady predictions based on conventional tunnel balance data through the calculation of derivative magnification factors. For all slant angles tested the results show that the quasi-steady prediction is a poor estimate of the real transient behaviour. In addition the slant angle is shown to have significant effect on the level of unsteadiness. The addition of Cpillar strakes is shown to stabilise the flow with even small height strakes yielding responses well below that of steady-state.

Static Stability and Ground Viscous Effect of a Compound Wing Configuration with Respect to Reynolds Number

Static stability is a main issue of a wing-in-ground effect (WIG) craft for safe takeoff and cruise mode of flight. In this study, the effect of ground boundary layers on aerodynamic behaviour and the height static stability of a compound wing ofWIG craft were numerically studied during ground effect. First, the principal aerodynamic coefficients of numerical analysis were validated by experimental data of the compound wing. Then, these coefficients of the compound wing were obtained for fixed and moving ground conditions. Consequently, the numerical results showed that viscous ground had some effects on lift and drag coefficients and lift-to-drag ratio, whereasmoment coefficient and centre of pressure of the compound wing had small variation due to removal of ground boundary layers.The present results clarified that the ground viscous effect can be changed slightly with Reynolds number. Also, the height static stability of the compound wing will be obtained and compared with the rectangular wing one. Based on the current results, the stability of the compound wing was higher than a common rectangular wing. In addition, the height static stability of both wings was strongly affected with ground clearance. It had slight reduction then fluctuated when Reynolds number was increased.

Development of delta wing aerodynamics research in Universiti Teknologi Malaysia low speed wind tunnel

This paper presents wind tunnel experiment on two delta wing configurations which are differentiated by their leading edge profiles: sharp and round-edged wings. The experiments were performed as a part of the delta wing aerodynamics research development in Universiti Teknologi Malaysia, low speed tunnel (UTM-LST). Steady load balance and flow visualization tests were conducted at Reynolds numbers of 0.5, 1, and 1.5 × 106, respectively. The flow measurement at low Reynolds number was also performed at as low as speed of 5 m/s. During the experiments, laser with smoke flow visualizations test was performed on both wings. The study has identified interesting features of the interrelationship between the conventional leading edge primary vortex and the occurrence and development of the vortex breakdown above the delta wings. The results conclude the vortex characteristics are largely dependent on the Reynolds number, angle of attack, and leading-edge radii of the wing.

Cavity Effect of Synthetic Jet Actuators Based on Piezoelectric Diaphragm

An active flow control technology known as synthetic jet actuator (SJA) is a zero-net mass-flux device to create pulsed jet that produces momentum to its surroundings and uses a vibrating diaphragm inside the cavity to generate an oscillatory flow through a small orifice. The performance of SJA depends on the design of an orifice and cavity, and oscillating membrane. SJA design based on piezoelectric diaphragm used in this project because of their size, lightweight, no need for external air supply, without the pipe complex, fast response time and low power consumption. This paper describes the cavity effect to SJA designs and experiments were performed to determine the air jet velocity produced through the orifice using a hot-wire anemometer at a different cavity thickness. The results demonstrate that the jet velocity increase would be better if the cavity thickness is reduced. However, more studies are needed to optimize the size of cavity and orifice for appropriate applications.

Evaluation of synthetic jet actuators design performance

Purpose – The purpose of this paper is to evaluate the synthetic jet actuator designs performance based on piezoelectric diaphragms that can be appropriately used for flow separation control.Design/methodology/approach – Design the synthetic jet actuators by means of estimating the several parameters and non‐dimensional parameters. Understanding the relationship and coupling effects of these parameters on the actuator to produce exit air jet required. Experiments were conducted to measure the exit air jet velocity using a hot‐wire anemometry and determine the good operational frequencies and voltages of the actuators for different cavity volume.Findings – The performance of synthetic jet actuator is not consistent to a particular given frequency and it depends on design configurations. Each actuator will give a very good speed for a certain frequency. The results show that the exit air jet velocity increases would be better if the cavity volume is reduced and if the input voltage is increased to certain ...

Design Parametric Study of a Compound Wing-in-Ground Effect. I: Aerodynamics Performance

AbstractThe configuration and service condition of a wing can influence the performance of wing-in-ground effect (WIG) craft. In this study, the aerodynamic performance of compound wings in ground effect was numerically investigated through a parametric design study. The compound wing is divided into three parts with one rectangular wing in the middle and two reverse taper wings with an anhedral angle at the sides. A NACA6409 airfoil was employed as a section of the wing. The design parameters included the span size, anhedral angle, and taper ratio plus two boundary conditions: ground clearance and Reynolds number. The three-dimensional, Reynolds-averaged Navier-Stokes (RANS) equations were solved numerically. A realizable k−e turbulent model was used to compute the effects of the turbulent flow over the wing surface. The computational results of the basic wing were compared with the experimental data of other published works. Next, the aerodynamic performance of the compound wings was computed for variou...

Effect of tail dihedral angle on lateral directional stability due to sideslip angles

This paper will describe the aerodynamic characteristic of complete aircraft equipped with conventional tail and V-tail configurations. Based on lateral-directional stability, the introduction of tail dihedral angle can significantly affect the yaw stability derivative of an aircraft. The wind tunnel test was conducted for sideslip angle, from -25◦ to 25◦ and the results were used to verify the CFD works. Good agreements were achieved at a lower sideslip angle which is below 15◦. Then, CFD will be used to study the flow field around the tail region and figure out the effect on the directional stability. This study found that during sideslip condition, conventional tail stall at a lower sideslip angle and only effective at lower sideslip condition. This study shows that the V-tail configuration provide an advantage at higher sideslip condition. The interactions of V-tail vertical tailplane slightly increase rolling stability thus causes the reductions in yawing motion.

Experimental aerodynamic characteristics of a compound wing in ground effect

Wing configuration is a parameter that affects the performance of wing-in-ground effect (WIG) craft. In this study, the aerodynamic characteristics of a new compound wing were investigated during ground effect. The compound wing was divided into three parts with a rectangular wing in the middle and two reverse taper wings with anhedral angle at the sides. The sectional profile of the wing model is NACA6409. The experiments on the compound wing and the rectangular wing were carried to examine different ground clearances, angles of attack, and Reynolds numbers. The aerodynamic coefficients of the compound wing were compared with those of the rectangular wing, which had an acceptable increase in its lift coefficient at small ground clearances, and its drag coefficient decreased compared to rectangular wing at a wide range of ground clearances, angles of attack, and Reynolds numbers. Furthermore, the lift to drag ratio of the compound wing improved considerably at small ground clearances. However, this improvement decreased at higher ground clearance. The drag polar of the compound wing showed the increment of lift coefficient versus drag coefficient was higher especially at small ground clearances. The Reynolds number had a gradual effect on lift and drag coefficients and also lift to drag of both wings. Generally, the nose down pitching moment of the compound wing was found smaller, but it was greater at high angle of attack and Reynolds number for all ground clearance. The center of pressure was closer to the leading edge of the wing in contrast to the rectangular wing. However, the center of pressure of the compound wing was later to the leading edge at high ground clearance, angle of attack, and Reynolds number.

Effects of Aircraft Tail Configurations on Sensitivity to Yaw Disturbances

A wind tunnel test was conducted to compare the characteristics of low speed stability and control for aircraft with conventional tail and V-tail configurations. Comparison was made in terms of static directional stability at selected test speed of 40 m/s, which corresponds to Reynolds number of 0.1622 x 106 based on the chord. Three types of simplified tail-only model were tested in Universiti Teknologi Malaysias Low Speed Wind Tunnel (UTM-LST). Results show that the V-tail configuration greatly affects the aerodynamic characteristics in directional stability as the side force and yaw moment tends to vary linearly with yaw angles up to 25 degrees, compared to conventional tail that has linear characteristics up to only 10 degrees yaw