Smooth Inlet Research Articles

Comparative aerothermal performance of two rotating triple-pass channels with lateral flow exit roughened by skewed ribs and pin-fins with and without internal effusion

The experimental study examines the aerothermal performances of two rotating triple-pass serpentine channels with the identical smooth inlet pass and downstream ribbed and pin-fin passes of different channel aspect ratios with and without the near-wall bypass flows between the ribbed and pin-fin passes. Relative to the static-channel references, the continuously elevated and the initially decreased and then increased trends of Nusselt number variations respectively propagate on the unstable and stable endwalls of each rotating pass when the rotation number increases. The buoyancy effect elevates local Nusselt number without altering the pattern of heat transfer distribution on each rotating endwall. In the rotating pin-in channels with (without) effusion, the combined Coriolis-force and buoyancy effects modify the average Nusselt numbers on their leading and trailing endwalls to 1–1.36 (0.99–1.41), and 1.04–1.54 (1.02–1.61) times the static-channel levels. The aerothermal performance indices of the pin-fin pass are elevated by effusion to 2.66–2.08 and 2.08–2.66 times non-effusion values at the static and rotating conditions.

Features of operation and hydraulic calculations

Issues related to the design and hydraulic calculations of the transit part of a closed tubular water supply structure of the siphon type are considered. The operating conditions of a siphon with rectangular pipes in the transition mode are estimated. Due to the formation of a hydraulic jump, the inlet section of the siphon pipes experiences increased hydrodynamic loads, leading to certain defects and destruction. The design of the siphon with two breaks along the length with a portal and a smooth inlet head or without it was modeled. As a result of modeling studies, the absence of a noticeable effect of the inlet head of the culvert on the length of the free-flow inlet section was established. It was revealed that the conditions of formation, the features of the hydraulic operation of the siphon, and the loads it experiences in the transient mode are largely determined by its design solutions. With the flooding of the inlet head, the flow of air into the pipe is hindered, and a transition mode of the second type is formed with a slight fluctuation in the water level in front of the structure upstream. The dependence of the location of the flow separation point with a decrease in the throughput of water on its value was revealed, which made it possible to obtain a graph of the dependence of the relative length of the free-flow section on the square root of the Froude number. A comparison was made with the results of studies by other authors, which showed an increase in the relative length in tubular structures of the siphon type in sections with reverse slopes at the same Froude numbers. Recommendations are given on the methodology for carrying out hydraulic calculation of tubular culverts for various purposes with minimal flow rates, and ways for further multifactorial studies of siphons on the reclamation network are indicated.

Оценка пропуска минимальных расходов воды сооружениями дюкерного типа мелиоративных систем

Issues related to the design and hydraulic calculation of the transit part of a closed tubular water supply structure of the siphon type is considered. The operating conditions of the siphon with rectangular pipes in the transition mode are evaluated, in which the entrance section of the pipes of the culvert structure experiences increased hydrodynamic loads, often leading to certain destructions. The siphon design was modeled with two breaks along the length with a smooth inlet head and without a head. During the experiments, the absence of infl uence of the inlet head of the tubular HTS on the length of the free-flow section was noted. It has been established that the conditions of formation and features of the hydraulic operation of the siphon in the transient mode are largely determined by its design features. With the flooding of the inlet head, the flow of air into the pipe is hindered and a transition mode of the second type is formed with a slight fluctuation of the water level in the upper pool. The dependence of the location of the point of separation of the flow with a decrease in the passing water flow rate on its value is revealed, which made it possible to obtain a graph of the dependence of the relative length of the non-pressure end section on the square root of the Froude number. A comparison was made with the results of studies by other authors, which showed an increase in the relative length in tubular HTS of the siphon type in sections with reverse slopes at the same Froude numbers. Recommendations are given on the methodology for carrying out hydraulic calculation of tubular structures of the siphon type with minimal flow rates.

Investigation of translation scheme turbine-based combined-cycle inlet mode transition

Smooth inlet mode transition is critical to turbine-based combined-cycle (TBCC) propulsion system. In this paper, we put forward a translation scheme TBCC inlet mode transition, that is the closing of turbine flowpath and opening of ramjet flowpath was conducted through the translation of mode transition device. The steady and unsteady flow characteristics of inlet mode transition were studied through wind tunnel tests and numerical simulations. The flow pattern and static pressure distribution from three-dimensional numerical simulations agreed well with wind tunnel tests results. According to wind tunnel tests and steady numerical simulations, smooth inlet mode transition can be achieved during translation scheme inlet mode transition. Based on the unsteady numerical simulation of inlet mode transition, as flight Mach number increased from 2.2 to 2.5, throat Mach number varied slightly from 1.35 to 1.36, which indicated that throat Mach number is not sensitive to freestream Mach number. The terminal shock wave generated from turbine flowpath oscillated around the leading edge of mode transition device until 2/4 mode and then moved downstream to turbine flowpath. In the meantime, ramjet engine took over and terminal shock wave moved from downstream ramjet flowpath to leading edge of mode transition device.

Flow field around a 5:1 rectangular cylinder using LES: Influence of inflow turbulence conditions, spanwise domain size and their interaction

Abstract The flow field around the rectangular cylinder with aspect ratio 5:1 has been widely investigated in recent literature as a prototype of reattached flow around elongated bluff bodies like bridge decks and high rise buildings. Due to the technical importance of such flows, many research works have been proposed aiming at studying the accuracy of available simulation techniques in reproducing the flow organization. When Large Eddy Simulations (LES) are considered, to the authors’ knowledge, the proposed contributions focused on perfectly smooth inlet conditions which, indeed, represent more an exception than a rule in Computational Wind Engineering. In the present paper, LES are performed aiming at reproducing the modifications occurring in the flow when turbulent inflow conditions are adopted. In order to synthetically produce the unsteady inlet condition, a divergence-free and spatially correlated fluctuations field is generated by means of the Modified Discretizing and Synthesizing Random Flow Generator technique. The obtained synthetic fluctuations are imposed in the computational domain by modifying the velocity-pressure coupling algorithm in order to avoid nonphysical pressure fluctuations. Two configurations, corresponding to mild and strong incoming turbulence levels, are investigated highlighting the role played by the spanwise domain size. Results are compared to experimental data showing good agreement between experiments and numerical simulations.

Experimental and numerical investigation of smooth turbine-based combined-cycle inlet mode transition

Smooth transition from turbojet to ramjet mode is critical to turbine-based combined-cycle (TBCC) propulsion system. Wind tunnel tests and numerical simulation were conducted to investigate the method of smooth inlet mode transition, and acquire corresponding inlet flow details. Steady-state pressure distribution was recorded in the experiment to evaluate inlet performance. Combined experimental and numerical investigation results indicate that smooth inlet mode transition can be achieved by keeping the total throttle ratio of the TBCC inlet constant. When the total throttle ratio is equal to 56%, the Mach number and the flow ratio of aerodynamic interface plane (AIP) would be basically equal to 0.22 and 0.50, respectively. Meanwhile, the terminal shock wave is located near the throat of the inlet during the mode transition. This paper puts forward the method of smooth mode transition of tandem-type turbine-based combined-cycle inlet and provides the flow details during this process.

Effects of Low Incoming Turbulence on the Flow around a 5 : 1 Rectangular Cylinder at Non-Null-Attack Angle

The incompressible high Reynolds number flow around the rectangular cylinder with aspect ratio 5 : 1 has been extensively studied in the recent literature and became a standard benchmark in the field of bluff bodies aerodynamics. The majority of the proposed contributions focus on the simulation of the flow when a smooth inlet condition is adopted. Nevertheless, even when nominally smooth conditions are reproduced in wind tunnel tests, a low turbulence intensity is present together with environmental disturbances and model imperfections. Additionally, many turbulence models are known to be excessively dissipative in laminar-to-turbulent transition zones, generally leading to overestimation of the reattachment length. In this paper, Large Eddy Simulations are performed on a 5 : 1 rectangular cylinder at non-null-attack angle aiming at studying the sensitivity of such flow to a low level of incoming disturbances and compare the performance of standard Smagorinsky-Lilly and Kinetic Energy Transport turbulence models.

Unsteady flow characteristic analysis of turbine based combined cycle (TBCC) inlet mode transition

A turbine based combined cycle (TBCC) propulsion system uses a turbine-based engine to accelerate the vehicle from takeoff to the mode transition flight condition, at which point, the propulsion system performs a “mode transition” from the turbine to ramjet engine. Smooth inlet mode transition is accomplished when flow is diverted from one flowpath to the other, without experiencing unstart or buzz. The smooth inlet mode transition is a complex unsteady process and it is one of the enabling technologies for combined cycle engine to become a functional reality. In order to unveil the unsteady process of inlet mode transition, the research of over/under TBCC inlet mode transition was conducted through a numerical simulation. It shows that during the mode transition the terminal shock oscillates in the inlet. During the process of inlet mode transition mass flow rate and Mach number of turbojet flowpath reduce with oscillation. While in ramjet flowpath the flow field is non-uniform at the beginning of inlet mode transition. The speed of mode transition and the operation states of the turbojet and ramjet engines will affect the motion of terminal shock. The result obtained in present paper can help us realize the unsteady flow characteristic during the mode transition and provide some suggestions for TBCC inlet mode transition based on the smooth transition of thrust.

ZnO Etching and Microtunnel Fabrication for High-Reliability MEMS Acoustic Sensor

This paper describes a technique for uniform step coverage of aluminum metal (Al) on ZnO film in the fabrication of MEMS acoustic sensor. The MEMS acoustic sensors were fabricated by etching ZnO layer in three different etchants: HCl, NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Cl with electrolytically added copper ions, and NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> OH with electrolytically added copper ions. For the first time, a technique is reported, which uses aqueous NH4OH solution with electrolytically added copper ions for etching of ZnO layer. For reliable operation of the device, the electrical testing of Al step coverage on ZnO layer was performed. The maximum currents that can be drawn across Al-deposited ZnO edge etched by HCl, Cu-added NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Cl, and Cu-added NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> OH were 40 mA, 2.5 A, and 3.0 A respectively, without any damage to the structures. The investigations show that uniform Al step coverage on ZnO layer is obtained in case of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> OH with electrolytically added copper ions. During fabrication of the device, a novel technique for building a microtunnel for pressure compensation was also developed. This microtunnel is used to compensate the pressure applied on the silicon diaphragm by connecting the cavity to the atmosphere. To realize the smooth inlet of microtunnel in the cavity, photoresist SU8 was used for patterning the cavity after microtunnel etching. The developed technique for microtunnel fabrication reduces the process complexity, providing improved yield of the device. The packaged device performed satisfactorily in the sound pressure level (SPL) of 120-160 dB over a wide frequency range of 30-8000 Hz. The maximum sensitivity of the sensor was measured as 380 μV/Pa.

A NOVEL HYBRID AIPO-MOM TECHNIQUE FOR JET ENGINE MODULATION ANALYSIS

A novel hybrid adaptive iterative physical optics- method of moments (AIPO-MoM) technique is presented for the electromagnetic analysis of jet engine structures that are both electrically large and complex in both stationary and dynamic cases. In this technique, the AIPO method is used to analyze the smooth inlet region, and the MoM method is used to analyze the electrically complex compressor region, including blades and a hub. It is e-cient and accurate by virtue of combining the respective merits of both methods. In the dynamic case, a concept for modifled impedance equation is proposed to reduce computational load. Numerical results are presented and verifled through comparison with Mode-FDTD and measured and commercial simulation packages results.

제트 엔진 산란 해석을 위한 하이브리드 IPO-MoM 기법

전기적으로 크면서 동시에 복잡한 구조인 제트 엔진의 산란 해석을 위해 하이브리드 IPO-MoM(Iterative Physical Optics-Method of Moments) 기법을 제시하였다. 이 기법에서 IPO 기법은 전기적으로 부드럽게 변하는 inlet 영역을, MoM 기법은 회전축과 회전날개를 포함한 전기적으로 복잡하게 변하는 영역을 해석하였다. 각 기법의 장점을 융합하여 상대적으로 효율적이고 정확한 해석이 가능하였다. 수치 결과를 제시하고 기존 Mode-FDTD, 측정 결과와 비교하여 제시한 기법을 검증하였다. A hybrid iterative physical optics-method of moments(IPO-MoM) technique is presented for the analysis of jet engine structures which are both electrically large and complex. In this technique, the IPO method is used to analyze smooth inlet region and the MoM method is used to analyze electrically complex region inclusive of blades and hub. It is efficient and accurate by virtue of combining the respective merits of both methods. Numerical results are presented and validated through comparison with Mode-FDTD and measured results.

Characteristics of developing free falling films at intermediate Reynolds and high Kapitza numbers

Experiments on developing free falling films have been carried out in a vertical rectangular channel, using smooth inlet conditions, with three liquids characterized by high Kapitza numbers, Ka (i.e. water, 1.5% butanol and 2.5% butanol solutions with surface tension 75, 50 and 40 mN/m, respectively) at intermediate Reynolds numbers ( Re L<400). Film thickness measurements supported by visual observations suggest that reduced surface tension significantly affects the inception of waves at the entrance region of the film. However, no significant qualitative difference is observed concerning developing wave patterns in the longitudinal direction, as large “tear-drop” type waves appear downstream in all cases, with the smaller Ka liquids being more unstable as expected. The new data show that above Re L∼200, the RMS values of film thickness fluctuations, beyond the wave inception region, tend to be nearly independent of Re L. Results concerning other typical falling film characteristics also show that above Re L∼200 (for the Re L range of the present experiments) the wave structure is weakly dependent on Re L beyond the wave inception region. The dominant disturbance frequencies on the wavy film surface as well as the wave celerity are in good agreement with earlier findings. Finally, results from previous linear stability analyses are compared with the new data showing in general satisfactory agreement especially with measurements corresponding to developing nearly two-dimensional waves.

The effect of initial conditions on the exit flow from a fluidic precessing jet nozzle

The fluidic precessing jet (FPJ) is a member of a family of self-excited oscillating jet flows that has found application in reducing oxides of nitrogen (NOx) from combustion systems in the high-temperature process industries. Its flow field is highly three-dimensional and unsteady, and many aspects of it remain unresolved. Velocity data, measured close to the exit plane, are presented for a variety of FPJ nozzles with three different inlet conditions, namely, a long pipe, a smooth contraction and an orifice. The results indicate that jet inlets that are known to have nonsymmetrically shedding initial boundary layers, namely those from the orifice or long pipe, cause jet precession to be induced more easily than the smooth contraction inlet, which is known to have a symmetrically shedding initial boundary layer. The nature of the exit flow is dominated by the degree to which a given configuration generates precession. Nevertheless, the three different inlet conditions also produce subtle differences in the exit profiles of mean velocity and turbulence intensity when the flow does precess reliably.

The influence of small tube diameter on falling film and flooding phenomena

Flooding experiments have been carried out in vertical small i.d. tubes (6, 7, 8 and 9 mm), using smooth inlet and outlet conditions, with air and two liquids (water and kerosene). Experimental data on free falling film characteristics have also been obtained, in the same test sections, which aid the interpretation of flooding phenomena. These new data suggest that the tube diameter strongly affects film flow development, possibly promoting wave interaction and damping. In turn, the wavy film evolution essentially determines flooding characteristics. At small liquid Reynolds numbers ( Re L<300) critical flooding velocities, U G, follow a trend already reported in the literature, i.e. decreasing with increasing liquid rate. However, at higher Re L the trend is reversed, i.e. increasing U G with increasing liquid rate. This has not been reported in the literature before and may be attributed to damping of waves. At still higher Re L, another region is evident in the flooding curves, characterized by nearly constant flooding velocity. The dominant mechanism in almost all cases is wave growth and upward dragging by the gas, initiated at the liquid exit.

Investigation of postflooding conditions in countercurrent gas–liquid flow

AbstractSystematic experiments were conducted to study the postflooding situation in air–water countercurrent flow in a tube of 0.025 m internal diameter with smooth inlet and outlet conditions for the two phases. The downflow rate of water and the pressure gradient were measured over a range of flow rates for test‐section lengths of 0.6, 1.2 and 2.0 m. Additional experiments were conducted with increasing and decreasing water flow rates at a constant air flow rate. The length of the test section or the way the flooding point was approached did not significantly affect the onset of flooding. The data show that, as the gas flow rate is increased, the pressure gradient can fall significantly in the postflooding situation due to depleting the downflow rate of liquid. Dimensionless correlations are proposed to calculate the downflow rate and the pressure gradient given for overall flow parameters.

Effect of tube diameter on flooding

This paper describes an experimental study on the effect of tube diameter on the mechanism of flooding in vertical gas–liquid countercurrent annular flow. Flooding experiments were conducted with three different tube inner diameters, namely, 25, 67 and 99 mm with smooth inlet and outlet conditions for air and water. The results indicate that the mechanism of flooding is qualitatively different in the small and the large diameter test sections. While flooding in the 25 mm diameter section occurred essentially by the upward movement of large waves created near the liquid outlet, no such waves could be seen in the 67 and the 99 mm diameter test sections. Here, flooding occurred by droplet carryover or by an unstable, churn-like motion in the liquid film. The results are compared with existing correlations. The effect of test section length on flooding was also investigated.

Drag Reduction and Its Application. Transition in Pipe Flow of Drag-Reducing Surfactant Solution.

Transition in pipe flow of drag reducing surfactant solution (C14TABr) has been studied experimentally. Two stainless pipes with inside diameter of 3.03 mm and 2.04 mm are used and the measurements of pressure drop and pressure fluctuations are carried out. In the case of surfactant solution, turbulence appears at higher Reynolds number than that for water and the flow is stabilized. In contrast to the flow of polymer solution, critical Reynolds number for surfactant solution doesn't decrease even in the case of smooth inlet condition, except for the case of high concentration solution. With an increase in the concentration of solution, critical Reynolds number becomes to be unaffected by the pipe inlet conditions. When the surfactant solution is used, frequency of pressure fluctuation becomes higher and amplitude of it becomes less than that for water.

Computational inlet-fairing effects and plume characterization on a hypersonic powered model

A three-dimensio nal computational study has been performed addressing issues related to the wind-tunnel testing of a hypersonic powered-simulation model. The study consisted of two related objectives. The first objective was to determine the three-dimensional flow effects on the aftbody created by fairing over the inlet; this was accomplished by comparing the computational fluid dynamics solutions of two closed-inlet powered configurations with a flowing-inlet powered configuration. Results at four freestream Mach numbers indicate that the exhaust plume tends to isolate the aftbody surface from most forebody flowfield differences, a smooth inlet fairing provides the least aftbody force and moment variation compared to a flowing inlet. The second objective was to predict and understand the three-dimensional characteristic s of exhaust plume development at selected points on a representative flight path of a single-stage-to-orbit vehicle. Results showed a dramatic effect of plume expansion onto the wings as the freestream Mach number and corresponding nozzle pressure ratio are increased. Nomenclature M = Mach number NPR = nozzle pressure ratio, pt,-}ejp*, p = pressure, Pa Re = Reynolds number, 1/m T = temperature, K a = angle of attack, deg AM = Mach number increment, see Figs. 3-5 p = density, kg/m3 Subscripts throat = conditions at the internal nozzle throat t, jet = jet total conditions wall = conditions at a solid wall boundary 00 = freestream conditions

The Two-Phase Critical Discharge of Initially Saturated or Subcooled Liquid

A nonequilibrium model is developed to describe the two-phase critical discharge of initially saturated and subcooled liquid through sharp edged inlet, constant area ducts with L/D ≥ 12. A similar model is proposed for smooth inlet geometries with L/D ≥ 0. The proposed solutions, which are based on the upstream stagnation conditions, exhibit excellent agreement with the published data which include water, Freon-11, and Freon-12 results.

Smooth Air Inlet and Maximum Lift Conditions for a Cascade of Thin Aerofoils

SUMMARY Schlichting's cascade functions are expressed as power series in terms of the blade solidity, which makes it possible to derive analytical expressions for the lift coefficient and velocity distribution of an arbitrary cascade of thin aerofoils for solidities of less than unity under smooth air inlet conditions. It is shown that, within the scope of the assumptions made, the angle of attack for shock‐free inlet conditions must be zero, irrespective of the cascade configuration, and that a symmetrical camber line will then yield the maximum lift coefficient. Expressions for this lift coefficient and for the corresponding velocity distribution are derived in terms of the maximum camber and cascade configuration. The analysis is based on Schlichting's cascade theory, and is intended primarily for application to fan blade design.