Engineering topics

Kalburgi, Vijay

Publications and source records attributed to Kalburgi, Vijay.

4 records

NASA NTRS1989

Goertler instability on an airfoil: Comparison of marching solution with experimental observations

Theoretical predictions based on the marching technique are compared with experimental observations on an airfoil with a concave region. Theoretical predictions of the wavelength of the most amplified Goertler vortex are in excellent agreement with the experimental observation for the range of chord Reynolds numbers from 1.0 to 3.67 million. In the convex zone, solutions from the marching technique showed that the initial counter-rotating vortex pairs lift off the surface and dissipate while another layer of vortex pairs of opposite rotation develops near the surface. This confirms the experimentally observed double peaked streamwise velocity perturbations. Furthermore, the streamwise velocity perturbations which dominate spanwise variation in the surface shear stress distribution shift by half a wavelength in the convex region. The experimental flow visualization photographs clearly confirm this phenomena.

Kalburgi, Vijay↗

NASA NTRS1988

A comparative study of theoretical methods on Goertler instability

Goertler vortices arise in boundary layers along concave surfaces due to centrifugal effects and these vortices in combination with Tollmien-Schlichting (TS) waves and crossflow vortices may play an important role in triggering early transition. There have been two distinct theoretical approaches to solve the problem. In the classical, normal-mode approach (NMA) the linear development of Goertler vortices is reduced to an eigenvalue problem. In the other method, initiated by Hall, the governing partial differential equations for the perturbations which are parabolic in the streamwise direction, are solved as an initial value problem. This method predicts multiple neutral curves depending on how and where the mean flow is perturbed, unlike the NMA where a unique but different neutral curve is predicted by each investigator. The present paper attempts to compare the two techniques and shows that mutually compatible results can be obtained when physically consistent assumptions are made.

Kalburgi, Vijay↗

NASA NTRS1987

Goertler instability on an airfoil

An effective computational scheme was developed to study the growth/damping of Goertler vortices along walls of variable curvature. Computational experiments indicate that when the amplification rates for the u-, v-, and w-perturbations are the same, the finite difference approach to solve the initial value problem and the normal mode approach give identical results for the Blasius boundary layer on constant curvature concave walls. The growth of Goertler vortices was rapid in the concave regions and was followed by sharp damping in the convex region. However, multiple sets of counter-rotating vortices were formed and remained far downstream in the convex region. The current computational scheme can be easily extended to more realistic problems including variable pressure gradients and suction effects.

Kalburgi, Vijay↗

NASA NTRS1987

Influence of suction and curvature on the growth of Goertler vortices on an airfoil

Laser velocimetry (LV) was used to study the development of Goertler vortices in a laminar boundary layer on a 1.83 m chord airfoil model. The vortex pattern was visualized using a sublimating chemical technique. A fixed, essentially uniform vortex spacing was observed throughout the test region for any given freestream velocity but the vortex wavelength varied significantly with change in freestream velocity. An appreciable, abrupt decrease in streak contrast indicated vortex damping in the convex region and was confirmed by disturbance functions determined from LV measurements. Moderate variation in suction levels did not alter the vortex spacing but appreciably modified the vortex strength. The experimental results on the growth of Goertler vortices along the concave surface and the effect of suction are compared with results from linear stability theory.

Mangalam, S. M.↗