Since nature has developed processes, objects, materials, and functions to increase its efﬁciency, it has the best answers when we seek to improve or optimize a system. Thus, the ﬁelds of bio-mimetic and bio-inspiration allow us to mimic biology or nature to develop methods for increasing the performance of all types of transportations involving land, sea, and air.
- Flapping Micro Aerial Vehicles (M. Sc. Thesis)
Many developments in aerospace science have originated from nature. One of these developments has been obtained through inspirations from ﬂying locomotion . Scientists have focused on motions of birds and insects in recent years in order to construct ﬂapping mechanisms with a higher performance. These ﬂapping mechanisms are extensively utilized in civil and military operations, including surveillance, reconnaissance, and sensing tasks in hazardous locations . By drawing inspiration from the black-headed gull, we designed and constructed a flapping mechanism which was able to create wing camber during the upstroke motion (Fig. 1). In our first study, we investigated the effects of wing bending deflection on the lift, thrust, and power consumption of the membrane flexible wing in forward flight. Results indicated that wing bending improves the aerodynamic performance. In our second research, we fabricated three wings representing different underlying structures, namely flexible membrane, rigid membrane, and airfoil, to study the effects of flexibility, thickness, and camber in hovering flight. Both experiments were performed for flapping frequencies ranging from 1.5 Hz to 6 Hz and 10 degrees angle of attack.
Fig.1 Black-headed gull vs. designed and constructed mechanism.
- Michelson RC (2004) “Novel approaches to miniature flight platforms” Proc IMechE, Part G: Journal of Aerospace Engineering, 218: 363–373.
- Steven Ho, Hany Nassef, Nick Pornsinsirirak, Yu-Chong Tai, Chih-Ming Ho (2003) “Unsteady aerodynamics and flow control for flapping wing flyers” Progress in Aerospace Science, 39: 635–681.
- Sinusoidal Leading-edge Wings
Due to the high maneuverability of humpback whales, many research works have been conducted to reveal secrets behind their excellent swimming performance. Scientists have shown that humpback whales use their sinusoidal leading-edge ﬂippers to increase their agility. Therefore, ﬂippers of humpback whales have been inspired by many scholars to improve the aerodynamic performance of unmanned aerial vehicles [2,3]. The goal of the research study we conducted at the wind tunnel lab at Ferdowsi University of Mashhad was to investigate the role of smart ﬂaps in the aerodynamics of sinusoidal and smooth leading-edge wings at low Reynolds numbers of 29,000, 40,000, and 58,000. Hence, four wings with different leading-edge conﬁgurations (smooth and sinusoidal), and different trailing-edge shapes (no ﬂap and smart ﬂap) were constructed (Figs. 1 and 2). Results showed that using trailing-edge smart flap in sinusoidal leading-edge wing delays the stall point compared to the same wing without flap.
Fig.1 Designed and prototyped wings: (a) smooth leading-edge wing without flap, (b) smooth leading-edge wing with smart flap, (c) sinusoidal leading-edge wing without flap, and (d) sinusoidal leading-edge wing with smart flap.
Fig. 2 View of model inside the wind tunnel.
- Van Nierop EA, Alben S and Brenner MP (2008) “How bumps on whale ﬂippers delay stall: an aerodynamic model” Physical Review Letters, 100: 054502.
- Hassanalian M, Salazar R and Abdelkeﬁ A (2019) “Conceptual design and optimization of a tilt-rotor micro air vehicle” Chinese Journal of Aeronautics, 32: 369–381.
- Goruney T and Rockwell D (2009) “Flow past a Delta wing with a sinusoidal leading edge: near-surface topology and ﬂow structure” Experiments in Fluids, 47: 321–331.
Renewable Energy (B.Sc. Thesis)
The burning of fossil fuels is the major cause of environmental pollution. Furthermore, oil and gas resources will be depleted within the next few decades . These problems necessitate paying special attention to renewable energy sources. Hydroelectricity is the most widely used form of renewable energy that benefits from the low cost of power generation, high reliability, simple design, and high efficiency in comparison to other renewable technologies [2,3]. However, traditional patterns of water management cannot cope with today’s needs including various objectives and constraints. Therefore, optimal management of hydropower systems seems to be necessary [4,5]. Using a dynamic programming method, the paper I published in International Journal of Renewable Energy Development was concerned about the optimization of the daily operation of a hydropower station. Produced profit and peak-shaving were the two objectives considered separately in this study. In another research study, we compared a conventional hydropower plant (HPP) and a pump-assisted one (PSP) in terms of different economic criteria, including the annual benefit from electricity sales (BA), net present value, benefit-cost ratio, payback time, and internal rate of return, under different levels of "natural inflow rate" and "electricity price change rate" as two key factors (Fig. 1).
Fig. 1 Comparison of PSP and HPP from annual revenue point of view.
- Hosseini SE, Andwari AM, Mazlan AW and Bagheri G (2013) “A review on green energy potentials in Iran” Renewable and Sustainable Energy Reviews, 27: 533–545.
- Egre D and Milewski JC (2002) “The diversity of hydropower projects” Energy Policy, 30(14): 1225-1230.
- Gaudard L and Romerio F (2014) “The future of hydropower in Europe: interconnecting climate, markets and policies.” Environmental Science and Policy, 37:172–181.
- Labadie J W (2004) “Optimal operation of multi reservoir systems: state-of-the-art review” Journal of water resources planning and management, 130(2), 93-111.
- Lu, B., Li, K., Zhang, H., Wang, W., & Gu, H. (2013) ”Study on the optimal hydropower generation of Zhelin reservoir” Journal of Hydro-environment Research, 7(4), 270-278.
Supersonic Air Intakes
Air intakes play a significant role in the thrust generation of supersonic engines. The main task of all intakes is to capture the required engine mass flow and increase the static pressure with the minimum possible total pressure loss. Moreover, an intake should provide a uniform flow for the subsequent component of the engine, which may be a compressor, fan, or combustion chamber, according to the engine type. Therefore, the proper design of an intake can enhance the overall efficiency of a vehicle. In our paper published in Journal of Aerospace Engineering, we investigated the effects of flow parameters, such as the flight Mach number and back pressure ratio, and also geometric parameters, including the intake exit area, spike tip angle, and overall length on performance parameters (Total pressure recovery (TPR), mass flow ratio (MFR), flow distortion (FD), and drag coefficient) of mixed compression and external compression intakes. We showed that FD is the most sensitive parameter to the geometric variations, while TPR and MFR were almost unchanged. In another research study presented in AIAA Propulsion and Energy 2019 Forum, we numerically studied the role of boundary layer suction applied at the cowl surface in the performance of an external compression supersonic air intake (Fig. 1). Results indicated that the intake with boundary layer suction has less distortion compared to the base intake. We also published a paper in IMECHE, Part G: Journal of Aerospace Engineering in which recent developments in boundary layer suction for high-speed air intakes have been reviewed.
Fig. 1 External compression intake equipped with bleed at cowl
In the last decade, it has been proven that the thermal conductivity of nanofluids (fuids+nanoparticles) is significantly higher than that of pure base fluids [1, 2]. This in turn can improve the energy efficiency of heat transfer systems. Additional benefits of nanofluids are high stability with low sedimentation , no flammability , smoothly flowing through micro channels without clogging and a reduction in pumping power in comparison with micro-size particles [5, 6]. In our research study published in Journal of Thermal Analysis and Calorimetry, we presented new models, namely enhancement factors, to theoretically calculate the heat transfer parameters of nanoﬂuids from thermophysical properties of the base ﬂuid and nanoparticle in the Rayleigh–Benard problem (Fig. 1). We conducted our research around critical Rayleigh numbers at which Rayleigh–Benard natural convection is started and flow transition to turbulence occurs. Results indicated that theoretical predictions can reach experimental data by using proper models for thermophysical properties.
Fig. 1 Schematic of Rayleigh–Benard natural convection
- Godson, L., et al., Enhancement of heat transfer using nanofluids—An overview. Renew Sustain Energy Rev, 2010. 14(2): p. 629-641.
- McGrail, B.P., et al., Metal-organic heat carrier nanofluids. Nano Energy, 2013. 2(5): p. 845-855.
- Ghadimi, A., R. Saidur, and H.S.C. Metselaar, A review of nanofluid stability properties and characterization in stationary conditions. International Journal of Heat and Mass Transfer, 2011. 54(17): p. 4051-4068.
- Li, Y., et al., A review on development of nanofluid preparation and characterization. Powder Technol., 2009. 196(2): p. 89-101.
- Murshed, S., K. Leong, and C. Yang, Thermophysical and electrokinetic properties of nanofluids–a critical review. Appl. Therm. Eng., 2008. 28(17): p. 2109-2125.
- Das, S.K., S.U.S. Choi, and H.E. Patel, Heat Transfer in Nanofluids—A Review. Heat Transfer Engineering, 2006. 27(10): p. 3-19.
Bluff Body Wakes
Bluff body wakes are considered as one of the most fundamental topics in fluid mechanics. Bluff bodies are widely used in industry and technology, including long-span suspension bridges, offshore risers, cables, skyscrapers, and wind turbine towers. When the Reynolds number exceeds a critical value, vortex shedding happens in the wake of bluff bodies, resulting in serious structural vibrations, acoustic noise, resonance, and a considerable increase in the value of mean aerodynamic fluctuations . Vortex shedding behind a square cylinder is demonstrated in the following animation at Re=100:
Therefore, vortex shedding is an undesirable phenomenon and scientists have made concerted efforts over the past decades to tackle this problem. These attempts can be generally divided into passive and active flow control methods. While active methods rely on imposing external energy to the fluid flow by a powered device, passive methods deal with geometry modifications. In my current research study, I am going to suppress the vortex shedding behind a square cylinder in a laminar flow regime using passive flow control methods.
- Choi H, Jeon W-P and Kim J (2008) “Control of Flow Over a Bluff Body” Annual Review of Fluid Mechanics, 40, 113-139.