Internal Drag Research Articles

An Investigation of Internal Drag Correction Methodology for Wind Tunnel Test Data in a High-Speed Air-Breathing Vehicle Using Numerical Analysis

AbstractAccurate understanding of aerodynamic characteristics is critical for air vehicle design. This study applies the impulse-momentum theorem to estimate internal drag of an asymmetric air vehicle. Both computational fluid dynamics (CFD) and wind tunnel tests were employed. Numerical analysis using STAR-CCM + was conducted across various Mach numbers, while wind tunnel tests were conducted under only specific Mach number conditions. The measured data from wind tunnel tests, which is considered representative, were compared with CFD plane-averaged values, indicating fairly good agreement. However, discrepancies arose when comparing CFD cell-averaged values with the plane-averaged values. To address this, a correction function was developed to describe the differences. It was observed that the ratio of internal drag coefficient from the cell-averaged values to that of the plane-averaged values followed an exponential function of Mach number. This approach allows wind tunnel data to be transformed into a form akin to cell-averaged values, enhancing internal drag estimation accuracy. Future research will explore additional methodologies to further refine and validate the proposed approach.

Evaluation of wear test on functionally graded metal-polymer tri-laminate composite interfaces of cooling-assisted friction stir additive manufacturing

In this study, a new friction stir welding (FSW) based additive manufacturing (AM) process called "cooling-assisted friction stir additive manufacturing (CA-FSAM)" was introduced to join sheets of metal-polymer hybrid structures (MPHS). Dry ice was introduced as the coolant. Thickness variations of the raw high-density polyethylene (HDPE) and 5083 aluminum alloy (Al5083) sheets were functionally graded at a rate of 0.75 mm from the former layer. The arrangement of layers in terms of thickness was arranged in the order of 3, 2.25, and 1.5 mm. Functionally graded metal-polymer tri-laminate composite fabricated with CA-FSAM technology was investigated using the pin-on-disk wear test. The results showed that mechanical locking between the layers affected the bond strength. Cross-sectional morphology examination revealed defect-free, strong joints. X-ray diffraction (XRD) results confirmed the formation of Mg2Si; however, the XRD peak was low, indicating a slight effect on the interface properties. Thermal gravimetric analysis (TGA)-Fourier transform infrared spectroscopy (FT-IR) characterization highlighted that the main evolved products during tri-laminate composite joining were CO, CC, CH3, CH2, and CH2. Oxidation occurred in the FTIR peak in the absorption band (1029.92 cm−1 to 1370.63 cm−1). Disk loading resulted in the buildup of an internal drag force that caused the dislocation/rupture of the CC or CH bonds. Defects, such as deep grooves, pits, and delamination at the interface, were observed in the composite specimen. The wear path was not visible in the worn composite material. The wear rate at 4 kg load on Al5083, HDPE, and metal-polymer tri-laminate composite specimens was 3.15 ± 0.22, 4.72 ± 0.36, and 3.42 ± 0.18 × 10−6 mm3/N. m, respectively.

Nonreciprocal interactions give rise to fast cilium synchronization in finite systems

Motile cilia beat in an asymmetric fashion in order to propel the surrounding fluid. When many cilia are located on a surface, their beating can synchronize such that their phases form metachronal waves. Here, we computationally study a model where each cilium is represented as a spherical particle, moving along a tilted trajectory with a position-dependent active driving force and a position-dependent internal drag coefficient. The model thus takes into account all the essential broken symmetries of the ciliary beat. We show that taking into account the near-field hydrodynamic interactions, the effective coupling between cilia even over an entire beating cycle can become nonreciprocal: The phase of a cilium is more strongly affected by an adjacent cilium on one side than by a cilium at the same distance in the opposite direction. As a result, synchronization starts from a seed at the edge of a group of cilia and propagates rapidly across the system, leading to a synchronization time that scales proportionally to the linear dimension of the system. We show that a ciliary carpet is characterized by three different velocities: the velocity of fluid transport, the phase velocity of metachronal waves, and the group velocity of order propagation. Unlike in systems with reciprocal coupling, boundary effects are not detrimental for synchronization, but rather enable the formation of the initial seed.

Uncertainty analysis method of internal drag measurement for flow-through model in high-speed wind tunnel

For aircraft with complex air intake and exhaust systems, the flow-through model simulating the internal flow passage is generally used to reduce the interference of internal and external flow fields when carrying out high-speed wind tunnel tests. The drag generated by the internal flow passage needs to be accurately measured and deducted from the full-model aerodynamic force, so as to obtain the aerodynamic characteristics of the aircraft to be tested. However, the existing internal drag measurement methods do not evaluate the uncertainty of the measurement results, which leads to the failure to evaluate the reliability of the flow-through model high-speed wind tunnel test results. This paper introduces the device and measurement method of internal drag of flow-through model. Based on GUM uncertainty analysis method, the analysis method of internal drag measurement uncertainty is established through strict mathematical derivation, which provides technical support for the evaluation of internal drag measurement uncertainty.

Effect of Flap Deflection on Single-Expansion-Ramp Nozzles Performance at Different Pressure Ratios

Experiments have been carried out to investigate the various performance characteristics of single-expansion-ramp nozzle with straight and deflected flap conditions for two different flap lengths. Experiments were performed at different nozzle pressure ratios (NPRs) ranging between 1.5 and 9. Wall static pressure measurements were made to estimate the various performance parameters, such as surface axial force, normal force, overall axial force, pitching moment, and thrust vectoring angles. Schlieren flow visualization technique was adopted to understand the internal shock-induced flow separation and shock patterns inside the nozzle under various NPRs. Flap deflection and NPR control the shock location through area variation, and thus the pressure distribution on the walls. At low NPRs, the internal drag force generated by deflected flap is lesser than that by straight flap, whereas at high NPRs the straight flap produces significantly higher surface axial thrust over the deflected flap. Behavior of normal force and pitching moment was affected by two factors: flap length and shock location. The straight flap shows significantly higher normal force than deflected flap. Hence, the thrust vectoring was better for straight flap nozzles compared to deflected flap nozzles, over the full range of NPRs tested. On the other hand, the gross thrust force performance is better for the straight flap for low NPRs and for the deflected flap for high NPRs. Overall, at high speeds, longer deflected flap appears to give better performance considering all the parameters, but will lead to heavier nozzle.

A novel experimental method to the internal thrust of rocket-based combined-cycle engine

• The method can be used to study high altitude performance of the RBCC engine. • There is a great moment to the engine when the rocket turns on. • The air mass flow rate is the most important factor to the RBCC engine. The rocket-based combined-cycle engine is considered as a promising scheme to achieve affordable and reusable space transportation. Under the ejector mode, the air mass flow rate is limited by aerodynamic chocking in the mixer of the engine. In other words, the air mass flow rate is determined by the downstream mixing. However for the requirement of critical air mass flow rate, the air stream supplying and the internal thrust measurement are difficult to conduct in the conventional ground experimental facilities. And more importantly, the critical thrust performance is also hard to obtain. A novel experimental facility is introduced in which the air stream is entrained from the ambient atmosphere. The inlet throat is large enough to make sure the inflow air is throttled by aerodynamic chocking in the mixer. In addition, a supersonic ejector is used to simulate the pressure environment at a high altitude. The internal thrust under different flight conditions can be calculated through the measured parameters in the experiments. The results show that the novel experimental facility can be used to study the thrust performance of rocket-based combined-cycle engine in ejector mode. The test precision is acceptable and the thrust difference between the test and the simulation is less than 8%. With the increase of the inflow Mach number, the engine internal drag under the cold flow condition rises as well as the specific impulse augmentation. The specific impulse augmentation could be 16.5% when the entrainment ratio is 1.88 at a simulated condition of H6.8 km / Mach 1.2.

Acceleration of Debris Flow Due to Granular Effect

Pore water pressure has been recognized as an important factor to enhance the mobility of debris flow moving in channel of very gentle slope. The creation and dissipation of pore water pressure are associated with interaction between grains. This study proposes a physical model for the pressure on mobility of flows with different granular configurations: the flow with overlying coarse-grained layer (i.e., inverse grading) and the flow with fully-mixed grains. The flow velocity is derived by the effective stress principle and the relationship between acceleration and pore water pressure is analyzed under different conditions. The results show that a high excess pore water pressure leads to high velocity of flow, and the pressure increases during the movement; and acceleration increases with time and flow depth under given pore water pressure. Moreover, compared with the flow with mixed grains, the flow with overlying coarse-grained layer is more effective to promote the excess pore water pressure and the liquefaction slip surface. Therefore, the internal drag reduction due to pore water pressure produces an acceleration effect on the flow.

Parameterizing Nonpropagating Form Drag over Rough Bathymetry

AbstractSlowly evolving stratified flow over rough topography is subject to substantial drag due to internal motions, but often numerical simulations are carried out at resolutions where this “wave” drag must be parameterized. Here we highlight the importance of internal drag from topography with scales that cannot radiate internal waves, but may be highly nonlinear, and we propose a simple parameterization of this drag that has a minimum of fit parameters compared to existing schemes. The parameterization smoothly transitions from a quadratic drag law () for low Nh/u0 (linear wave dynamics) to a linear drag law () for high Nh/u0 flows (nonlinear blocking and hydraulic dynamics), where N is the stratification, h is the height of the topography, and u0 is the near-bottom velocity; the parameterization does not have a dependence on Coriolis frequency. Simulations carried out in a channel with synthetic bathymetry and steady body forcing indicate that this parameterization accurately predicts drag across a broad range of forcing parameters when the effect of reduced near-bottom mixing is taken into account by reducing the effective height of the topography. The parameterization is also tested in simulations of wind-driven channel flows that generate mesoscale eddy fields, a setup where the downstream transport is sensitive to the bottom drag parameterization and its effect on the eddies. In these simulations, the parameterization replicates the effect of rough bathymetry on the eddies. If extrapolated globally, the subinertial topographic scales can account for 2.7 TW of work done on the low-frequency circulation, an important sink that is redistributed to mixing in the open ocean.

Design and experimental validation of a specialized pressure-measuring rake for blended wing body aircraft’s unconventional inner flow channel

The internal drag of the unconventional inner flow channel of blended wing body aircraft must be measured accurately to correct the air intake effect of the blended wing body flow-through model in wind tunnel tests. In this study, the pressure distribution of the inner flow channel under the interaction of internal and external flows was obtained through numerical simulation. A specialized pressure-measuring rake was designed based on the numerical results, and a validation test was conducted in a 2.4 m × 2.4 m transonic wind tunnel. Compared with the flow in traditional inlets/nozzles, the flow in the unconventional inner channel in the current research is asymmetric, the distortion index is higher, and the internal drag is more sensitive to flow changes. The wind tunnel test results have a good correlation with the numerical results, and the repeatability of the test results is satisfactory, indicating that the measurement accuracy and precision of the pressure-measuring rake are acceptable. The design method of the specialized rake is feasible, and it can be used to guide the measurement of complex flow in unconventional inner flow channels of blended wing body aircraft.

Experimental and numerical heat transfer from vortex-injection interaction in scramjet flowfields

ABSTRACTAir-breathing propulsion has the potential to decrease the cost per kilogram for access-to-space, while increasing the flexibility of available low earth orbits. However, to meet the performance requirements, fuel-air mixing inside of scramjet engines and thermal management still need to be improved.An option to address these issues is to use intrinsically generated vortices from scramjet inlets to enhance fuel-air mixing further downstream, leading to shorter, less internal drag generating, and thus more efficient engines. Previous works have studied this vortex-injection interaction numerically, but validation was impractical due to lack of published experimental data. This paper extends upon these previous works by providing experimental data for a canonical geometry, obtained in the T4 Stalker Tube at Mach 8 flight conditions, and assesses the accuracy of numerical methodologies such as RANS CFD to predict the vortex-injection interaction.Focus is placed on understanding the ability of the numerical methodology to replicate the most important aspects of the vortex-injection interaction. Results show overall good agreement between the numerical and experimental results, as all major features are captured. However, limitations are encountered, especially due to a localised region of over predicted heat flux.

ON DETERMINATION OF INTERNAL DRAG WHEN TESTING MODELS OF INTEGRATED AIRCRAFT WITH DUCTS

The problem of determining the internal drag in ramjet integrated layouts is considered. It is shown that the standard technique for internal drag adjustment in tests of aircraft models with a duct developed for axisymmetric layouts can lead to differences in adjustment values when applied to the integral layout of the lifting body with an under-fuselage ramjet. It is proposed to include the aerodynamic drag of the external compression inlet braking body in the aerodynamic characteristics of the airframe, as well as to determine the internal drag only within the limits of the duct itself (i.e., from the mouth to the nozzle exit) and the need to measure the flow parameters in both the nozzle exit section and at the duct mouth. Calculation estimates of the internal drag of the integral layouts using the Navier-Stokes equations are given.

Devising Carbon Nanotube, Green Tea, and Polyaniline Based Nanocomposite plus Investigating Its Rheological together with Bactericidal Efficacies.

Subsequently, engines are designed to operate at low viscosity engine oils. Low viscosity oils take less power from engines, bring down the internal drag, cut the fuel consumption, and ultimately improve the engine’s efficiency. Considering this focus, an approach has been made to formulate a multiwalled carbon nanotube based green tea and polyaniline nanocomposite, that is, GT/MWCNT/PANI, and incorporate it in engine oil (base fluid). The objective was to reduce the viscosity of engine oil by examining the effects of the constant shear rate and varying shear rates on the viscosity of Castrol class 15W-40 engine oil. The investigation was performed at a constant temperature of 25 °C for a fixed volume fraction of 0.1% GT/MWCNT/PANI in engine oil on the experimental setup rheometer from Anton Paar Series. Primordial findings revealed that, at a constant shear rate of 100 s–1, engine oil viscosity was lowered from 0.221000 to 0.001402 Pa·s, that is, 99% reduction in viscosity of the engine oil, after incorporating the GT/MWCNT/PANI nanocomposite. Furthermore, a new correlation has been proposed considering the experimental and theoretical models with an average percentage error of 0.040%. Also, at varying shear rates, up to 90 s–1, the shear viscosity of nanofluid decreases significantly, leading to shear-thinning behavior of the nanofluid, while at a shear rate of >90 s–1, it shows Newtonian behavior. Besides, the ternary nanocomposite with 0.2 wt % GT/MWCNT/PANI also showed significant bactericidal effects with the zones of inhibition of 19, 18, and 15 mm against Gram-negative (Pseudomonas aeruginosa, Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria, respectively, as measured using the well diffusion method.

Research and Application of Solvent-Free Internal Drag Reducing Epoxy Coating for Non-Corrosive Gas Transmission Service

The developed coating performance meets the corresponding technical specification by using modified epoxy resin and E51 epoxy resin as resin system to optimize the system viscosity and flexibility, adding reactive diluents owning good flexibility, using modified alicyclic amine curing agent with good flexible performance and corrosion resistance, optimizing assistant system concluding defoaming agent, levelling agents and so on. Application adaptability, concluding viscosity, thixotropy, sag resistance and pot life, were also studied under different temperatures, considering that these parameter are important to spraying process. The dry film thickness can be adjusted between 60-150 μ m by modulating spraying application parameters, meanwhile, the flat smooth film meets internal drag reducing coating technical parameters requests. The product were successfully applied in China key projects. According to field pilot test, application attention items were also discussed.

MYBP-C Phosphorylation Accelerates Sarcomere Shortening as Thin Filaments Slide through the C-Zone

Myosin Binding Protein-C (MyBP-C) is a 140-150 kDa thick filament protein located in the middle third of each sarcomere, i.e., the C-zone, and is likely a key regulator of contraction. Phosphorylation of MyBP-C occurs at 4 residues within its N-terminus and PKA phosphorylation of MyBP-C in hearts is associated with faster cardiac muscle twitch dynamics (Tong et. al. Circ. Res. 2008). Here we investigated potential mechanisms by which MyBP-C phosphorylation regulates myofilament function. We utilized slow-twitch skeletal muscle fibers since PKA phosphorylates slow skeletal (ss)MyBP-C but not (ss)troponin I. Permeabilized rat slow-twitch fibers were mounted between a force transducer and motor, and calcium activated to elicit ∼30% maximal force. We measured rates of force development and transient force overshoots following a slack re-stretch maneuver and monitored sarcomere shortening during load-clamps. Following PKA, force development rates increased ∼40% and there was a near-doubling in the magnitude of transient force overshoot. We also observed faster shortening velocities at all loads following PKA treatment; this may arise from (i) faster cross-bridge cycling rates, (ii) greater number of cross-bridges during load clamps, and/or (iii) attenuation of internal drag imposed by binding of MyBP-C to actin. To address these mechanisms, we quantified sarcomere length shortening as thin filaments traversed into the C-zone. Before PKA, there tended to be a slowdown as sarcomeres shortened from ∼3.05 to 2.90 µm. After PKA, sarcomeres shortened a considerably greater distance during similar load clamps and, at times, shortening even accelerated as thin filaments slid through the C-zone. Overall these results suggest MyBP-C phosphorylation speeds sarcomere shortening and power output by a combination of faster cross-bridge cycling kinetics, recruitment of cross-bridges, and reduction in drag forces as thin filaments slide through the C-zone.

Drag prediction method of powered-on civil aircraft based on thrust drag bookkeeping

A drag prediction method based on thrust drag bookkeeping (TDB) is introduced for civil jet propulsion/airframe integration performance analysis. The method is derived from the control volume theory of a powered-on nacelle. Key problem of the TDB is identified to be accurate prediction of velocity coefficient of the powered-on nacelle. Accuracy of CFD solver is validated by test cases of the first AIAA Propulsion Aerodynamics Workshop. Then the TDB method is applied to thrust and drag decomposing of a realistic aircraft. A linear relation between the computations assumed free stream Mach number and the velocity coefficient result is revealed. The thrust losses caused by nozzle internal drag and pylon scrubbing are obtained by the isolated nacelle and mapped on to the in-flight whole configuration analysis. Effects of the powered-on condition are investigated by comparing through-flow configuration with powered-on configuration. The variance on aerodynamic coefficients and pressure distribution is numerically studied.

Internal Drag Evaluation for a Through-Flow Nacelle Using a Far-Field Approach

The main objective of this research is to propose a method for decomposing the total drag of a nacelle into external, internal, and wake drag. From a bookkeeping agreement, the internal drag (i.e., the drag generated inside a nacelle) is the engine manufacturer’s responsibility and is not to be included in the aircraft’s total drag. Consequently, computing the internal drag is mandatory for the airframe and engine constructors concerned and can be achieved either experimentally or by computational-fluid-dynamics analysis. Up to now, aerodynamic engineers have used a near-field approach to compute the internal drag using computational-fluid-dynamics analysis, but this method has serious drawbacks, including its dependency on the accurate location of the stagnation line. The new method proposed here has been applied to multiple two- and three-dimensional test cases, and results show that it is independent of the location of the stagnation line and yields accurate results that agree well with experimental and empirical data. Results also show that the wake drag of a through-flow nacelle is caused by the flow passing through the nacelle and so needs to be added to the internal drag.

Numerical Simulation of Internal Flow Drag Reduction with Triangular Riblet Surface

Computational fluid dynamics (CFD) numerical simulation is adopted to analyze the drag reduction ability of triangular riblet on tube internal flow. The resistance characteristic of smooth tube and tube covered with triangular riblet surface are compared, and the near wall flow structure over smooth surface and riblet surface are investigated. Based on the simulation analysis, the drag reduction mechanism of riblet surface is studied. Results show that the characteristic dimension of riblet section, i.e., height (h) and width (w) are main factors affecting drag reduction, suggesting that the riblet structure can be optimized according to the actual application condition.

Modelling and Analysis of Turbofan Engines Under Windmilling Conditions

Engine windmilling and relight performance is a matter of safety in aviation. Two of the most important properties that engine designers must have a feeling for, even from the very early design stages, are the windmilling engine mass flow and internal drag. However, only empirical approaches are available so far to perform such studies. This work is focused on the development and validation of a first principles methodology for the prediction of the aforementioned properties, based on the simple frictional flow theory. Considerations about the modeling of the pressure loss factors are also made. Validation of the method is carried out by comparing the predicted windmilling drag and mass flow against test data of several high-bypass civil engines for a typical range of operating conditions. The results compare favorably with the test data, proving the robustness and reliability of this approach. Fully dimensionless parameters are defined to describe the windmilling performance, independent of the engine design and operating conditions. This research contributes to the preliminary engine development phases, because engine studies can be conducted using minimal geometrical information, allowing for a reliable prediction of the windmilling properties.

Test Technique for the Measurement of Intake Drag of Air-Breathing Vehicles

KNOWLEDGE of intake drag is important in estimating the performance of the aerospace vehicle. The contribution to the intake drag is mainly due to the external and internal flow through the intake and termed as external and internal drag. External drag is mainly composed of drag due to cowl, diverter, and spillage of flow (pre-entry drag), while the internal drag is due to the wall skin friction and pressure distribution on the walls of the duct. Various components of the drag associated with a typical intake of an air-breathing vehicle are shown in Fig. 1. It is possible to estimate the internal drag in the absence of any flow separation while the estimation of external drag is difficult particularly when the intake is operating in subcritical condition. At this operating condition of intake, experimental method is the only source to determine the intake drag. Hitherto, drag due to intake alone is measured having the intake specially mounted to the forebody of the fuselage and front portion of intake forming a metric part with a balance.Available test techniques demand a special balance and suitable modifications to the intake module [1]. This is cumbersome and involves more time and additional cost towards design, fabrication and calibration of new balance. As an alternative, a test technique developed and patented for the direct measurement of after body drag in the base flow wind tunnel [2–4] is used to demonstrate the usefulness of this technique for the measurement of intake drag in a limited Mach number range. An important feature of this test technique (Fig. 2) is that it facilitates simultaneous measurements of total pressure recovery profiles of the duct flow as well as intake drag for the different mass flow conditions.

Internal Losses and Flow Behavior of a Turbofan Stage at Windmill

The flow through a high-bypass ratio fan stage during engine-out conditions is investigated, with the objective of quantifying the internal losses when the rotor is at “windmill.” An analysis of altitude test data at various simulated flight Mach numbers shows that the fan rotational speed scales with the engine mass flow rate. Making use of the known values of the nozzle coefficients, we deduce the stagnation pressure loss of the fan stage, which rises significantly as the mass flow rate increases. In order to better understand this behavior, numerical simulations of the fan stage were carried out. The calculated losses agree well with the test data, and it is found that the bulk of the stagnation pressure loss occurs in the stator. A detailed examination of the flow field reveals that the relative flow leaves the rotor at very nearly the metal angle. Moreover, the rotational speed of the fan is such that the inboard sections of the fan blade add work to the flow, while the outboard sections extract work from it. The overall work is essentially zero so that the absolute swirl angle at the rotor exit is small, causing the stator to operate at a severely negative incidence. A gross separation ensues, and the resulting blockage of the stator passage accelerates the flow to high Mach numbers. The highly separated flow in the vane, together with the mixing of the large wakes behind it are responsible for the high losses in the vane. Based on the simulation results for the flow behavior, a simple physical model to estimate the windmill speed of the rotor is developed and is found to be in good agreement with the test data. The utility of this model is that it enables the development of a procedure to predict the internal drag at engine-out conditions, which is discussed.