Icebergs Drift and Decay (PhD thesis)

Fig. 1: photo credit: Daniel Albert (SINTEF)

Bio-inspired Engineering (M. Sc. Thesis)

 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.

• Experimental investigation of flapping mechanism of the black-headed gull in forward flight
• The role of wing bending deflection in the aerodynamics of flapping micro aerial vehicles in hovering

By drawing inspiration from the black-headed gull (Fig. 1), we investigated the effects of wing bending deflection on the lift, thrust, and power consumption of the membrane flexible wing in forward flight. Results, which were published in IMECHE, Part G: Journal of Aerospace Engineering, indicated that wing bending improves the aerodynamic performance. In another research published in IMECHE, Part G: Journal of Aerospace Engineering, we fabricated wings representing different underlying structures, namely flexible membrane and rigid membrane, 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.


• Effects of smart flap on aerodynamic performance of sinusoidal leading-edge wings at low Reynolds numbers

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. The goal of the research study we conducted at the wind tunnel lab at Ferdowsi University of Mashhad (Fig. 2) 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, we constructed four wings with different leading-edge configurations (smooth and sinusoidal), and different trailing-edge shapes (no flap and smart flap) (Fig. 3). Results, which were published in IMECHE, Part G: Journal of Aerospace Engineering, showed that using trailing-edge smart flap in the sinusoidal leading-edge wing delays the stall point compared to the same wing without flap (Fig .4).

Fig. 2: View of model inside the wind tunnel.
Fig. 3: Designed and prototyped wings:(a) wing A (smooth leading-edge wing without flap), (b) wing A1 (smooth leadingedge wing with smart flap), (c) wing B (sinusoidal leading-edge wing without flap), and (d) wing B1 (sinusoidal leading-edge wing with smart flap).
Fig. 4: Variations of lift to drag ratio with angle of attack at Reynolds number of 40,000

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. 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 .

• Optimal Operating Scenario for Polerood Hydropower Station to Maximize Peak Shaving and Produced Profit

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 (Fig. 1). Produced profit and peak-shaving were the two objectives considered separately in this study. The results showed that the optimal water management of the case study through charging and discharging the reservoir at the appropriate times leads to 4% increase in the produced profit (Fig. 2).

Fig.1: schematic view of a hydro power plant

Fig. 2: comparison of the optimal power generation scenarios for two objective functions of Produced profit and peak-shaving

• A novel map for deciding on the type of a hydro power plant

In another research study published in Proceedings of the Institution of Civil Engineers-Energy, 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 (NPV), 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. 3).


Fig. 3: comparison of PSP and HPP from different economic viewpoints: (a) BA; (b) NPV

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:


•  Suppression of vortex shedding behind a square cylinder confined in a diverging channel

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. Confinement is one method to passively controlling the vortex shedding behind bluff bodies. However, this technique is often accompanied with a significant drag increase as a penalty. This problem has been tackled in my recent research study, published by Ocean Engineering, by confining the bluff body in a diverged channel. It was shown that the vortex shedding behind a square cylinder is completely suppressed if it is confined in channels with 0.26 ≤ Divergence Ratio ≤ 0.45 at Re=100. Furthermore, the drag coefficient of the square cylinder in the channel with divergence ratio of 0.26 is 18.85% lower than the unbounded cylinder. Flow field around the unbounded square cylinder and around the cylinder confined in a smooth channel and also a diverged channel is demonstrated in Fig.1.

Fig. 1. Flow field around the square cylinder confined in a smooth channel and a channel with DR=0.26, and around the unbounded cylinder.


• A review of experiments on stationary bluff body wakes

In another study published in Physics of Fluids, we extensively reviewed experimental studies dealing with the wake of isolated stationary bluff bodies (Fig. 2). After briefly recalling the pioneering works in this domain, we focsed on recent research conducted with the latest experimental methods and techniques. The review encompasses a range of topics, including the effects of bluff body geometry (non-circular cross sections and non-uniformity in spanwise direction), steady and unsteady (periodic and non-periodic) inflow conditions, surface proximity (rigid wall, confinement, and water free surface) and non-Newtonian fluids.

Fig. 2: (Left) Leonardo da Vinci, sketches of the flow around bluff bodies partially immersed in a water stream (1513). (Image mirrored for text reading) (Right) Henri Benard first cinematography of alternating vortices (Karman–Benard wake) past a cylinder towed in water.13

Supersonic Air Intake

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 to 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.

• Performance Evaluation of External and Mixed Compression Supersonic Air Intakes: Parametric Study

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 (Fig. 1). We showed that FD is the most sensitive parameter to the geometric variations, while TPR and MFR were almost unchanged (Fig. 2).

Fig. 1: geometry and shock pattern of the intakes simulated in this study at design condition: (a) external compression intake; and (b) mixed compression intake

Fig. 2: flow field in the subsonic diffuser after the internal normal shock at M∞ = 2 and BPR = 3: (a) external compression intake; and (b) mixed compression intake (derived from the contours of the axial velocity).


• Performance Enhancement of an External Compression Intake by the Boundary Layer Suction

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. 3). Results indicated that the intake with the boundary layer suction has less distortion compared to the base intake (Fig. 4).

Fig. 3: boundary layer suction applied at the cowl surface

Fig. 4: contours of axial density gradient at M∞=2.2 and BPR=3.0; (a) primary intake, and (b) intake with bleed


• Boundary layer suction for high-speed air intakes: A review

We also reviewed recent developments in boundary layer suction for high-speed air intakes, which was published in IMECHE, Part G: Journal of Aerospace Engineering.

• Investigation of Corner Rounding Effects on the Performance of a Supersonic Air Intake abstract

In a paper which was presented in 16th international conference of Iranian Aerospace Society, we simulated flow numerically through and around a mixed-compression intake to investigate effects of corner rounding on intake performance at free stream Mach numbers of 1.8, 2 and 2.2 and at zero degrees angle of attack. Furthermore, we studied the effects of different Mach numbers and back pressures. We showed that applying fillet can significantly improve performance parameters, including flow distortion and mass flow ratio (Fig. 5). 

Fig. 5: contours of Mach number for different fillet radiuses of curvature at  and , (left) No Fillet (right) with fillet



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. 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.

• Theoretical study of nanofluids behavior at critical Rayleigh numbers

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 the 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. 2).

Fig. 1: Schematic of Rayleigh–Benard natural convection.

Fig. 2: Variation of Nusselt number around critical transition Rayleigh numberfor SiO2–water nanofluid with nanoparticle diameter of 100 nm and T = 60 C (a) present model, (b) Kim model, (c) Abouali model, and (d) Sharma model