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Delaying transition in a Blasius boundary layer with finite compliant panels
(Fourth International Symposium on Bifurcations and Instabilities in Fluid Dynamics (BIFD),, 2011-07-18) Bori Ige; Zhao, .X.; Yeo, .K. S.
Compliant surfaces have been shown to be a promising passive control measure for controlling and
delaying boundary layer transition in various theoretical studies [1-2]. In this paper, we report on a
recent study we have done on the evolution of pulse-initiated disturbance wavepackets over one or
more finite-length compliant panels. The broadband nature of a wavepacket offers a central advantage
in permitting natural selection of most dominant waves to operate through the sum of its growth
processes. This may be helpful in identifying the critical waves and key processes that are involved at
the various stages in natural transition. The initiation, evolution and final breakdown of wavepackets
into the incipient turbulent spots in a Blasius boundary layer was modelled by Direct Numerical
Simulation (DNS) briefly described in [3]. The comparative evolution and transition performance of
three cases are discussed here, namely the rigid-wall case, a single-panel wall and a two-panel wall.
In all cases, a fixed vertical-directed delta pulse of small amplitude was initiated at the point x /
349.4, where 2.3182103m is the displacement thickness of the boundary layer at the initiation
point.
The evolution and breakdown of the wavepacket in a Blasius boundary layer on a rigid wall has
already been reported in [3]. For the single-panel case, a finite section of the wall from x / 450 to
762 was replaced by a tensioned membrane on a viscoelastic foundation, whose properties were
designed to inhibit the development of compliant-wall modes. The simulation results showed that, the
upstream intervention by the finite compliant panel effectively delayed the onset of the incipient
turbulent spot by a distance of about 100 cm ( x / 430). This represents an approximately 30%
increase in the transition distance measured from the point of wavepacket initiation. Spectral study
indicated that the relatively short membrane panel was able to effectively attenuate the primary 2-D
Tollmien-Schlichting (TS) wave mode so that resultant wavepacket after the panel was dominated by
a pair of oblique waves. Subharmonic secondary instabilities [4-5], which are responsible for
nonlinear disturbance wave amplification on a rigid wall, were thus inhibited by the absence or near
absence of the 2-D TS wave mode. Staggered Λ-structures and streamwise streaky structures similar
to those found in the rigid wall case were observed for the single-panel case, but much further
downstream. A second tensioned membrane panel of the same length was added at x / 1359-1658
to form the two-panel case. The last stage of the present simulation shows the wavepacket arriving the
location x / 2000 in a perfectly laminar form ( max | u | /U 0.05 ) – this already represents an
increase in transition distance of about 50% over the corresponding rigid-wall case. The eventual
breakdown location will be further downstream as the wavepacket has not displayed the usual
structural features that signify imminent breakdown. This study has shown the efficacy of short
compliant panel(s) in controlling and delaying transition.
Evolution of wavepacket over short compliant panels in a Blasius boundary layer
(American Physical Society (APS), 65th Annual Meeting Division of Fluid Dynamics (DFD), 2012-11-18) Bori Ige; Yeo, .K. S.; Dou, .H-S.
Compliant surface has been proved in various theoretical
studies as a promising tool in delaying transition. This study concerns
our recent work carried on the evolution of pulse-initiated disturbance
wavepackets over finite-length compliant panels in a Blasius boundary
layer by direct numerical simulation (DNS) method. A finite section of
the wall was replaced by a tensioned membrane on a damped foundation.
By comparing with the rigid wall case, the upstream intervention
by a finite compliant panel was found to effectively delay the onset of
the incipient turbulent spot – an increase of about 40% in the transition
distance with respect to the initiation point was obtained. Transition
distance to the occurrence of the incipient turbulent spot was increased
further to about 75% relative to a rigid wall when a second compliant
panel was introduced. Spectral analysis shows the important role of the
fundamental 2D modes in wavepacket evolution and the roles played by
compliant panels in transition delay.
DEVELOPMENT OF A BRAKE DRUM MODEL WITH FINS INCORPORATION FOR HEAT DISSIPATION ENHANCEMENT
(5th Multi-disciplinary academic conference, Ahmadu Bello University, Zaria. January 11, 2018. Pp. 190 – 205., 2018-01-11) Bako, .S.; Bori Ige
Extreme heat within an automobile brake drum could cause brake failure which could as well lead to death of passengers and lost of properties. One of the ways to dissipate heat faster from an automobile brake drum is by incorporating fin on the outer surface of the brake drum as pointed out in many literatures. This work concerns converting 1/10 0f the overall height thickness of the brake drum into fins for effective heat dissipation by both conduction and convection. During the modified brake drum development process, necessary fin design formulae were taken into account. Modeling and simulation analysis were carried out using Solidworks (2013) software, followed by validation using theoretical Finite Element analysis. The minimum temperatures obtained from the simulation analysis were 4935K and 4927K for the existing and the modified brake drum model respectively. While maximum displacements obtained from the simulation analysis were 5142×10−5𝑚𝑚 and 5102×10−5𝑚𝑚 for the existing and the modified brake drum model respectively. This implies that the modified brake drum have improved strength and better heat dissipation than the existing model. This is as the result of the circumferential arrangement of the fins on the outer surface of the brake drum.
Modelling of the Temperature Distribution in a Cooled Aeroderivative Gas Turbine Blade with Cooling Holes
(2021 Sustainable Engineering and Industrial Technology Conference, Faculty of Engineering, University of Nigeria, Nsukka, Enugu State, 22nd -25th June, 2021. Pp. 171- 176., 2021-06-22) Mohammed, .O.; Nasir, .A.; Bori Ige; Hassan, .B.
Aero-derivative gas turbines have found extensive applications, as mechanical drives and medium sized utility power plants
on o shore platforms and in petrochemical industries; because of its high operating temperature and pressure, it has a
higher e ciency. The high operating conditions of the engine makes it necessary to adopt e ective cooling techniques to
achieve the required creep life and attain reliability. This makes the study of the heat transfer within the gas turbine blade
essential. This study models the temperature distribution in a cooled aero-derivative gas turbine blade. A numerical model
was developed from the interpolation of the Newton’s law of cooling equation and the Alternating Direction Implicit (ADI)
scheme. A MATLAB solver was generated for the heat transfer problem based on the selected boundary conditions and
designed cooling parameters of model engine: GE PGT25+ aero-derivative gas turbine. It was found that there was e ective
heat transfer from the blades to the cooling air with a cooling e ectiveness of 0.5, and the temperature gradient within the
blade was within safe operating limits not exceeding the melting point of the blade material. It was deduced that the ADI
strategy accurately compute temperature distributions within the blade, in time and space, thereby making it suitable for heat
transfer design computations for complex thermodynamic systems like the gas turbine engine.
Modelling of Thermo-mechanical Fatigue in an Aeroderivative Gas Turbine Blade made of Inconel 738LC
(Faculty of Engineering, University of Nigeria, Nsukka, Enugu State, 2021-06-22) Orah, .M.; Nasir, .A.; Bori Ige; Hassan, .B.
The hot gas section of the gas turbine engine, especially the blades, are usually subjected to high thermal and mechanical
loading, as a result su er thermo-mechanical fatigue. The design process usually involves appropriate selection of the turbine
blade materials, it is therefore necessary to carry out thermo-mechanical fatigue studies on gas turbine blades to predict blade
life. This study models the thermo-mechanical fatigue on gas turbine blade made of nickel based super alloy IN738LC.
Simulink was used to develop thermal models to compute the heat transfer coe cient on the cold and hot sides of the blade,
and a stress model to compute the centrifugal tensile stress. The heat transfer coe cients, Reynold’s number, and Stanton
number at di erent velocities on the hot and cold section of the blade was obtained. The relationships between the Heat
transfer coe cient and the Reynold’s number with the change in velocities at the hot and cold sections of the blade was also
established. The stress model computed the centrifugal tensile stress acting on the blade at 31.41GPa.The heat transfer and
stress models are therefore necessary for TMF calculations to predict the creep life of the blade to prevent engine failure.