Traversing System Research Articles

Strategies for High-Accuracy Measurements of Stage Efficiency for a Cooled Turbine

Abstract Gas turbines are used in a broad range of aerospace and land-based applications from power generation to aviation, and their usage is projected to continue to grow. It is therefore critical to improve turbine efficiency thereby reducing fuel consumption and carbon emissions. Demonstration of new efficiency-increasing technologies requires efficiency measurements that are accurate and repeatable. The Steady Thermal Aero Research Turbine (START) Laboratory at the Pennsylvania State University uses a unique 360-deg traversing system for temperature and pressure probes with redundant torque measurements to quantify thermal efficiency for a single-stage cooled test turbine. Flows in the full annulus have been analyzed and compared with subsector traverse segments centered at different circumferential positions to determine the appropriate sector size. The results from this investigation indicate that the full 360-deg measurement is recommended to minimize variation in calculated stage efficiencies. This study also compares the circumferential variations in thermodynamic and mechanical efficiency definitions, finding that the thermodynamic efficiency calculation results in a higher accuracy for full exit plane measurements. A statistical analysis was then performed to determine the number of 360-deg traverse measurements required to achieve a precision uncertainty at most that of the bias uncertainty. This study establishes guidelines to streamline experimental procedures by limiting the necessary test count per day per operating condition to five measurements for at most four test days. Following these procedures establishes a bias of ɛb = 0.19 points, resulting in a total uncertainty of at most ɛt = 0.32 points.

Adaptation of von Karman Institute for Fluid Dynamics’ Isentropic Compression Tube Facility for High-Speed Low-Pressure Turbines Testing

Abstract This paper presents the commissioning of a newly designed High-Speed Low-Pressure Turbine (LPT) stage, operating at transonic exit Mach numbers and low Reynolds numbers, typical of modern geared turbofan (GTF) applications. The work falls within the scope of the Clean Sky 2 project SPLEEN (Secondary and Leakage Flow Effects in High-speed Low-pressure Turbines), which consists of an extensive experimental characterization of LPTs for GTFs. Geometries and measurements will constitute a valuable open-access database for the validation of simulation methods and data analysis tools. At first, the characteristics of the research turbine are illustrated. The LPT stage is designed with an equal number of stationary vanes and shrouded rotor blades. The upstream and downstream hub cavities are purged and feature engine-realistic rim seals. The nominal operating condition of the stage is reported, along with a set of off-design conditions, obtained by varying rotor speed and purge mass flows. The second part of the paper describes the substantial revamping of the CT3 large-scale compression tube at Von Karman Institute for Fluid Dynamics, traditionally employed for high-pressure turbine testing, now adapted to host a high-speed LPT stage. The third section is an overview of the time-averaged and fast-response instrumentation. The test article is heavily instrumented, to maximize the amount of acquired data, while minimizing the number of blowdown tests. The dataset for each operating conditions includes aerothermal measurements in the annulus flow, in the hub cavities and in the shroud labyrinth seal. In addition, this section presents the design of an in-house traversing system for continuous probe traversing during the test. Finally, the outcome of the commissioning phase is discussed, with particular emphasis on the operating conditions stability, as well as on the inlet and cavity injection uniformity. The commissioning of a traversing system for continuous probe traversing during the short-duration test is also discussed.

Aeroacoustics of finite wall-mounted square cylinders in pressure gradient flows

Flow-induced noise produced by finite wall-mounted cylinders (FWMCs) is a major noise source for aircraft landing gear, rail pantographs and submarine appendages. These applications often encounter flows with various pressure gradients, however, there is little information in the literature on the effects of pressure gradients. Our recent work has demonstrated that the presence of a pressure gradient can significantly affect the near-wake flow structures of a square FWMC with a low aspect ratio of 2.4, thereby suppressing/enhancing the vortex-shedding tones. The current study extends this work to square FWMCs with varying aspect ratios, focusing on the role that aspect ratio plays in the noise generation of square FWMCs in pressure gradient flows. Experiments were undertaken using the open-jet pressure-gradient test rig in the UNSW anechoic wind tunnel, where the square FWMC model was immersed in flows with favourable-, near-zero-, and adverse-pressure gradients at a width-based Reynolds number of 28800. The square FWMC model was installed on a traversing system to realize the change in cylinder aspect ratio. Inside the test model, a series of channels and surface pressure taps were created to measure the unsteady surface pressure using a remote microphone technique. Far-field noise and unsteady surface pressure signals were simultaneously acquired to characterize the combined effects of aspect ratio and pressure gradient on the far-field noise production and reveal the noise generation mechanisms.

A continuously scanning spatiotemporal averaging method for obtaining volumetric mean flow measurements with stereoscopic PIV

In this study, a variation of the stacked stereoscopic PIV technique is proposed to perform fully volumetric (3-dimensions, 3-components) measurements of average flow fields within a single experiment through the usage of an automated traversing system that continuously scans the SPIV light sheet over a linear path. The simultaneous measurement of the traverse location and the laser Q-switch pulse enables the automated assignment of instantaneous PIV fields to known physical coordinates, enabling spatiotemporal averaging in post-processing to obtain volumetric measurements of a flow field. This method provides a trade-off between spatial resolution of the volume measurements and statistical convergence of the spatiotemporal averages, enabling volumetric measurements under challenging experimental conditions where only stereoscopic PIV is viable. A comparison with the more traditional temporal averaging method and planar PIV is presented to demonstrate the capabilities and limitations of this technique in realistic, challenging experimental setups. It is found that the spatiotemporal averaging convergence behavior differs slightly from the traditional temporal averaging for the wake of a bluff body model, however relative errors lower than two standard deviations can still be attained. Thus, this technique presents a viable alternative for rapid 3D reconstruction of averaged flow fields that can provide invaluable insight of various flow topologies.

Medical Image Encryption Based on Josephus Traversing and Hyperchaotic Lorenz System.

This study proposes a new medical image encryption scheme based on Josephus traversing and hyperchaotic Lorenz system. First, a chaotic sequence is generated through hyperchaotic system. This hyperchaotic sequence is used in the scrambling and diffusion stages of the algorithm. Second, in the scrambling process, the image is initially confused by Josephus scrambling, and then the image is further confused by Arnold map. Finally, generated hyperchaos sequence and exclusive OR operation is used for the image to carry on the positive and reverse diffusion to change the pixel value of the image and further hide the effective information of the image. In addition, the information of the plaintext image is used to generate keys used in the algorithm, which increases the ability of resisting plaintext attack. Experimental results and security analysis show that the scheme can effectively hide plaintext image information according to the characteristics of medical images, and is resistant to common types of attacks. In addition, this scheme performs well in the experiments of robustness, which shows that the scheme can solve the problem of image damage in telemedicine. It has a positive significance for the future research.

ABB Robotic Laser Doppler Anemometry Measurements With RobotStudio® With An Open Wind Channel And An Ellipsoid

Laser Doppler anemometry is a state-of-the-art non-invasive experimental flow measurement technique. Traditionally used linear traversing units can only change the position of the measurement probe, but cannot change the orientation of the probe. A six degrees of freedom robot can simplify and fasten up the pose planning and measurement process real-offline. A developed LDA software plug-in for RobotStudio is used to real-offline plan and perform flow measurements in an open wind channel (flow rate = 300 m³/h) with an ellipsoid (diameter y=z = 140 mm and x = 40 mm). In 25 mm, 20 mm, 15 mm, 10 mm, 5 mm and 2 mm orthogonal distance of the ellipsoid surface the tangential velocity component is determined. Accuracy and repeatability of the robot-LDA system is found and compared to the traditional linear traversing system. Results show a positive velocity gradient towards the axis of the wind channel with a velocity range of 4.4 – 20.3 m/s. At 25 mm distance the tangential velocity is in the range of 4.4 – 12.5 m/s, at 20 mm 7.6 – 17.5 m/s, at 15 mm 12.1 – 19.7 m/s, at 10 mm 16.5 – 20.1 m/s, at 5 mm 19.0 – 20.2 m/s and at 2 mm 18.3 – 20.3 m/s. In positive y and negative z-direction, a reduction of the tangential velocity component is found in all measurements. At a distance of 25 mm, the measurement surface is slightly outside to the wind channel inlet (diameter = 80 mm). The closer the measurement surface is at the wind channel axis, the higher is the wind channel axial component. Robot-LDA average accuracy of 13 µm and repeatability of 10 µm is in the range of the linear traversing unit where the accuracy is 20 µm and the repeatability is 6 µm. The robot-LDA measurement system is an alternative to the existing linear-LDA with the advantages of real-offline robot path planning for arbitrary surfaces requiring six degrees of freedom probe placement.

Wind Tunnel Testing of Yaw by Individual Pitch Control Applied to Wake Steering

The yaw control of horizontal-axis wind turbines is the key point for wake redirection, which is expected to provide an improvement in the balance between wind farm production and loads. For multi-MW upwind wind turbines, there are substantially two possibilities for obtaining a desired demanded yaw angle: using yaw actuators or Individual Pitch Control (IPC). A detailed balance of the pros and cons of both approaches requires in-depth studies. On these grounds, this work is a comprehensive experimental characterization of the yaw by individual pitch control (yaw-by-IPC). The experiments are conducted at the R. Balli wind tunnel of the University of Perugia on a fully instrumented wind turbine scaled model, named G1, developed by the Technical University of Munich. The objective of the study is twofold: assessment of the performance of the yaw-by-IPC in terms of yaw tracking capabilities and impact on power, loads, and actuators usage; analysis of its impact on the shed wake. The wake has been characterized on a plane parallel to the rotor at a distance of 1.82 diameters by imposing several steady yaw references, while wind intensity measurements have been performed through a traversing system hosting a hot wire anemometer. Each target of the analysis has been characterized for the yaw-by-IPC and for the control based on yaw actuation, in order to perform a comparison. With laminar inflow, it results that the yaw-by-IPC follows very well the demanded reference, even with a slight improvement in the case of dynamic yaw reference, and no power losses are visible. Concerning the wake shed by a yawed G1 with yaw-by-IPC, a higher flow speed is observed immediately behind the windward side of the rotor than with geared yaw actuation. It results, therefore, that yaw-by-IPC applied to a yawed wind turbine may increase the available wind power at a downstream machine.

Virtual four sensor fast response aerodynamic probe (FRAP®)

This paper introduces the new fast response aerodynamic probe (FRAP®), which was recently developed at the ETH Zurich. The probe provides time-resolved, three-dimensional flow measurements using the virtual four sensor technique. Two probes work in tandem, being comparable to a pair of pneumatic needle probes. The first probe, being yaw angle sensitive, is positioned in three circumferential positions. The second probe being pitch angle sensitive is brought into exactly the same position as the first probe. The resulting set of four measurements is phaselock-averaged to one specific rotor trigger position. Then the reduced data sets are combined to four calibration coefficients, which are then further processed to determine the unsteady flow vector. The results consist of yaw and pitch flow angles as well as the total and static pressure. The outer diameter of the cylindrical probe head was miniaturized to 0.84mm, hence probe blockage effects as well as dynamic lift effects are reduced. The shape of the probe head was optimized in view of the manufacturing process as well as aerodynamic considerations. The optimum geometry for pitch sensitivity was found to be a cylindrical surface with the axis perpendicular to the probe shaft. The internal design of the probes led to a sensor cavity eigen frequency of 44 kHz for the yaw sensitive and 34kHz for the pitch sensitive probe. The steady aerodynamic characteristics of the probe were measured using the free jet probe calibration facility of the laboratory. The full set of calibration surfaces is given. Data acquisition is done with a fully automated traversing system, which moves the probe within the test rig and samples the signal with a PC-based A/D-board. An error analysis implemented into the data reduction routines revealed acceptable accuracy for flow angles as well as pressures for many turbomachinery flows. Depending on the dynamic head of the application the yaw angle is accurate within ±0.35° and pitch angle within ±0.7°. Finally, a comparison of time averaged results to five hole probe measurements is discussed.

Liquid Spray Characterization Using Phase /Doppler Technique.(Dept.M)

Spray characteristics of three liquids, water. diesel fuel, and kerosene. sprayed vertically downward in a transparent squared section rube which is accessed with an exhauster through Doppler Particle a pressure swirl atomizer, have been evaluated by means of Phase Analyzer (PIDPA) system. The experimental apparatus is accessed with a traversing system which enables to make complete scan. radially and axially, for the spray cone. Different pressure differentials across the nozzle are applied to study their effect on spray characteristics. Measurements of drop let mean diameter, droplet size distribution . droplet mean velocity, liquid volume flux and droplet number density have been carried out. Experimental results showed that the droplet size increases and droplet axial mean velocity decreases as the radial distance from spray axis increases. Also, as the axial distance from the nozzle plane increases. the droplet axial mean velocity decreases for the used liquids. the droplet mean diameter and liquid volume flux decrease for both water and diesel fuel but deviation is observed for kerosene. and the droplet number density increases for all used liquids. As the pressure differential across the nozzle increases, both droplet mean diameter and liquid volume flux decreases. and the axial mean velocity increases. for the used liquids. Data analysis shows that the mass median diameter to Sauter mean diameter ratio is affected by the pressure differential across the nozzle, and by Rosin-Rammler exponent, which is a measure of the width of distribution . kerosene, always. has the smallest drop let mean diameter, and water, in most of cases. has the largest mean diameter. Sometimes, diesel fuel competes water having the largest mean diameter.

Dew point measurement at the Stuttgart University ATF

Highly efficient conditioning of the air supplied to the test vehicle is a vital task of an altitude test facility (ATF). The time needed to achieve stable conditions as well as the required amounts of energy and other supplies to achieve those conditions are means to measure the effectiveness of the ATF operation. Optimizing the operation of single facility components only delivers local optima but not a total operational optimum. Hence, the optimized operation of highly interlinked groups of components delivering a defined functionality has to be achieved. A thorough understanding of the operational characteristics of the components is a prerequisite for such an optimization. The complex systems required for cooling the air supplied to test vehicles down to high-altitude temperature conditions is an example for such a complex optimization task. In a first step, the operational envelope of one of the Stuttgart ATF air coolers has been characterized experimentally. This included the analysis of the startup procedures. A new measurement setup to determine the dew point within the Stuttgart University Altitude Test Facility has been implemented for this purpose. Experiments were conducted to measure the dew point using a precise hygrometer. A radial traversing system was implemented to enable measurements at different positions downstream of the air cooler. Since the determination of the dew point takes place in a wide temperature range, a probe for sampling and conditioning of the air was developed. The measured data are of high quality. The achieved results form the basis of the operational optimization of the Stuttgart ATF air cooler system.

Magnetic accumulation of kinetic energy from a reciprocating mechanical system for a dynamic behaviour improvement

This paper presents a magnetic means of accumulating kinetic energy from a traversing rod (TR) used to guide yarn during winding processes on rotor spinning machines. A passive magnetic system for accumulating kinetic energy at the reversal points of reciprocating motion is introduced, and its unique repulsive magnetic force is described in relation to the specific traversing-motion characteristic. The magnetic damping force phenomenon and preconditions for its application in the machine are also defined and discussed. We also show magnetic field optimisation by means of pole-piece geometry modification to obtain a magnetic force characteristic that closely approximates the required motion characteristic. Thus, the efficiency of kinetic-energy accumulation at the reversal points of the reciprocating motion of the TR is increased. The utilisation of an eddy-current effect on the accumulator body to apply the magnetic-damping phenomenon for vibration reduction is also described. The results of this work demonstrate the promise of the system using modern rare-earth compound-based magnets applicable not only to the studied traversing system but also to various mechanical devices as a non-contact means of reducing deformation and vibration. The developed and experimentally verified mathematical models presented here represent a useful tool for further optimisation of specific applications in the field of mechanics.

Experimental investigation of the unsteady aerodynamics of FOWT through PIV and hot-wire wake measurements

This work presents a selected set of results from an extensive experimental campaign aimed at characterizing the wake aerodynamics of a floating offshore wind turbines (FOWT) in dynamic conditions. The campaign was carried out in the Politecnico di Milano 14m x 4m atmospheric boundary layer test section, under UNAFLOW project (UNsteady Aerodynamics of FLoating Wind turbines). Wake measurements were carried out either through hot-wire anemometers with a traversing system as well as through Particle Image Velocimetry (PIV) technique. A 1/75 scale model of the DTU 10 MW reference wind turbine was adopted, which was mounted on a hydraulically actuated mechanism imposing sinusoidal surge motion at different frequencies and amplitudes, and for different tip speed ratios λ. Selected results are reported with the aim of giving a first interpretation of the novel set of measurements, also completing previous measurements conducted by the authors, to put the basis of a more comprehensive understanding of unsteady aerodynamics of FOWT for control and wind farm purposes.

Measurement of spectra over the Bolund hill in wind tunnel

AbstractWe have determined the normal Reynolds stresses and spectra of the wind velocity over a 1:115 scale mock‐up of the Bolund hill. The experiment was run in a neutral boundary layer wind tunnel using 3‐component hot‐wire velocimetry, 2‐component particle image velocimetry, and a high‐precision traversing system. Spectra have been determined at different points along transects at 2 and 5 m height above ground level. The experiment was run for 270° wind direction and for two Reynolds numbers, and , based on the maximum height of the hill and the free wind speed at this height. Our results show how the normalized power spectral density changes over the hill. The analysis of the normalized streamwise spectrum at 2 m height, just after the escarpment, reveals that part of the energy is concentrated in the interval of normalized frequencies nh≈0.01−0.02, which could be a signature of a weakened “flapping” phenomenon described in the literature for flows over forward facing steps. The departure of the spectra slope in the inertial subrange, from the value −5/3, was found to be correlated with the hill geometry.

Enhanced Central System of the Traversing Rod for High-Performance Rotor Spinning Machines

Abstract The paper deals with the improvement of central traversing system on rotor spinning machines, where rectilinear motion with variable stroke is used. A new system of traversing rod with implemented set of magnetic-mechanical energy accumulators is described. Mathematical model of this system is analysed in the MSC. Software Adams/View and verified by an experimental measurement on a real-length testing rig. Analysis results prove the enhancement of devised traversing system, where the overall dynamic force is reduced considerably. At the same time, the precision of the traversing movement over the machine length is increased. This enables to increase machine operating speed while satisfying both the maximal tensile strength of the traversing rod and also output bobbin size standards. The usage of the developed mathematical model for determination of the optimal number and distribution of accumulators over the traversing rod of optional parameters is proved. The potential of the devised system for high-performance rotor spinning machines with longer traversing rod is also discussed.

Wind tunnel testing of the DeepWind demonstrator in design and tilted operating conditions

The DeepWind Project aims at investigating the feasibility of a new floating vertical-axis wind turbine (VAWT) concept, whose purpose is to exploit wind resources at deep-water offshore sites.The results of an extensive experimental campaign on the DeepWind reduced scale demonstrator are here presented for different wind speeds and rotor angular velocities, including also skewed flow operation due to a tilted rotor arrangement. To accomplish this, after being instrumented to measure aerodynamic power and thrust (both in streamwise and transversal directions), a troposkien three-bladed rotor was installed on a high precision test bench, whose axis was suitable to be inclined up to 15° with respect to the design (i.e. upright) operating condition.The experiments were performed at the large scale, high speed wind tunnel of the Politecnico di Milano (Italy), using a “free jet” (open channel) configuration. The velocity field in the wake of the rotor was also fully characterized by means of an instrumented traversing system, to investigate the flow distribution downstream of the test section.Special care is taken in the description of the experimental set-up and of the measured data, so that the present results can be used as a benchmark for the validation of simulation models.

A compact in-blade five hole pressure probe for local inflow study on a horizontal axis wind turbine

Understanding local inflow conditions on a wind turbine blade on an operating wind turbine can further understanding of aerodynamic variations and help predict loads on the turbine. Turbine blades are generally designed with a two-dimensional steady approach, however the real wind conditions are highly three-dimensional (3D) and unsteady. Detailed measurements are not common for validating aerodynamic models. The aim of this theoretical and experimental study is to build, calibrate, install and test a compact in-blade five hole pressure probe system to be used to retrieve these measurements. Wind tunnel calibration of the five hole pressure probe has been successfully completed using an automated traversing system over a ±45° range, with 5° increments. Error analysis showed that the multi-zone pressure coefficient data reduction approach is the most suitable for this application. This approach not only extends the measurable local inflow angles up to ±70°, but also it allows any reference pressure for differential pressure readings. A new data acquisition system (DAQ) internal to a rotating small wind turbine blade section was developed. Space limitations resulted in a custom built DAQ of very contained dimensions. This included, among others, five pressure transducers on a printed circuit board, a 16 bit analog to digital converter, an Arduino microcontroller, and a Bluetooth transceiver to transmit the data wirelessly to the main computer. The new blade section was designed and 3D-printed in such a way that the DAQ instrumentation could be easily accessed and, at the same time, had an acceptable structural solidity. A series of tests were conducted on a 3.4 m diameter wind turbine in a large scale wind tunnel in order to assess the correct functioning of the probe system. As expected, the inflow measurement obtained while the turbine was operating under yawed conditions showed a periodically oscillating inflow vector. The period of this variation was the same as the period of the rotor rotation.

H233 直膨方式地中熱ヒートポンプの熱交換性能 : 室内機側での性能評価(一般講演(13))

A ground source heat pump (GSHP) is paying attention as one of the energy saving technologies. The purpose of this study is to investigate a heat exchanging performance of a ground source heat pump using direct expansion method. The direct expansion method for heat exchange will be more efficient comparing with the conventional indirect heat exchange method. However it is difficult to measure the calorimetric value of the heat pump system using direct expansion method because the refrigerant becomes two phase flow. Therefore, we evaluated the calorimetric value around the indoor unit of the heat pump system. We also improved the accuracy of the measurement of the velocity distribution using the traversing system of the hot wire anemometer.

A Time Efficient Adaptive Gridding Approach and Improved Calibrations in Five-Hole Probe Measurements

Five-Hole Probes (FHP), being a dependable and accurate aerodynamic tool, are an excellent choice for measuring three-dimensional flow fields in turbomachinery. To improve spatial resolution, a subminiature FHP with a diameter of 1.68 mm is employed. High length to diameter ratio of the tubing and manual pitch and yaw calibration cause increased uncertainty. A new FHP calibrator is designed and built to reduce the uncertainty by precise, computer controlled movements and reduced calibration time. The calibrated FHP is then placed downstream of the nozzle guide vane (NGV) assembly of a low-speed, large-scale, axial flow turbine. The cold flow HP turbine stage contains 29 vanes and 36 blades. A fast and computer controllable traversing system is implemented using an adaptive grid method for the refinement of measurements in regions such as vane wake, secondary flows, and boundary layers. The current approach increases the possible number of measurement points in a two-hour period by 160%. Flow structures behind the NGV measurement plane are identified with high spatial resolution and reduced uncertainty. The automated pitch and yaw calibration and the adaptive grid approach introduced in this study are shown to be a highly effective way of measuring complex flow fields in the research turbine.

Design and implementation of a three axis digitally controlled traverse system for flow surveys in a drying chamber

The current paper describes the design and development of a pc-controlled three axis traverse system that aims to serve extensive velocity and temperature measurements into the drying chamber of a laboratory scale convective dryer. The traversing gear design has been conducted based on the convective dryers specific experimental requirements and limitations. The fabricated traversing gear uses a trapezoidal lead screw-nut assembly supported by linear ball bearings, coupled with bipolar stepper motors for positioning in three dimensional spaces. A custom drive system solution was selected for achieving accurate motor control, paired with computer software developed using the LabVIEW graphical programming environment. The functionality of the traversing system was experimentally verified by testing mechanical and electronic assemblies, but also by determining the per axis positioning error. Keywords: Fluid Flow Measurement, Digital Control, Motion Control, Displacement Control, Electromechanical Devices.

Control of stationary cross-flow modes in a Mach 3.5 boundary layer using patterned passive and active roughness

AbstractSpanwise-periodic roughness designed to excite selected wavelengths of stationary cross-flow modes was investigated in a three-dimensional boundary layer at Mach 3.5. The test model was a sharp-tipped$1{4}^{\circ } $right-circular cone. The model and integrated sensor traversing system were placed in the Mach 3.5 supersonic low disturbance tunnel (SLDT) equipped with an axisymmetric ‘quiet design’ nozzle at NASA Langley Research Center. The model was oriented at a$4. {2}^{\circ } $angle of attack to produce a mean cross-flow velocity component in the boundary layer over the cone. The research examined both passive and active surface roughness. The passive roughness consisted of indentations (dimples) that were evenly spaced around the cone at an axial location that was just upstream of the first linear stability neutral growth branch for cross-flow modes. The active roughness consisted of an azimuthal array of micrometre-sized plasma actuators that were designed to produce the effect of passive surface bumps. Two azimuthal mode numbers of the passive and active patterned roughness were examined. One had an azimuthal mode number that was in the band of initially amplified stationary cross-flow modes. This was intended to represent a controlled baseline condition. The other azimuthal mode number was designed to suppress the growth of the initially amplified stationary cross-flow modes and thereby increase the transition Reynolds number. The results showed that the stationary cross-flow modes were receptive to both the passive and active patterned roughness. Only the passive roughness was investigated at a unit Reynolds number where transition would occur on the cone. Transition front measurements using the Preston tube approach indicated that the transition Reynolds number had increased by 35 % with the subcritical wavenumber roughness compared with the baseline smooth tip cone, and by 40 % compared with the critical wavenumber roughness. Based on the similarities in the response of the stationary cross-flow modes with the active roughness, we expect it would produce a similar transition delay.